refactor: rename internal Fai* design system + fai_ helpers to chain

The Studio design system, widgets and helpers carried a Fai* / fai_
prefix (FaiSpace, FaiColors, FaiTheme, FaiLog, 17 fai_*.dart files, the
faiBinary* l10n keys). Studio is the Ch∆In product, so rename them to
Chain* / chain_ — carefully preserving English fail/failure/failed.
Also fix stale references: the 'fai' binary in l10n strings -> 'chain',
FAI_* env vars (FAI_BIN/DATA_DIR/MODULES_DIR/TODAY/BOOTSTRAP_TOKEN) ->
CHAIN_*, fai_platform -> fai_chain, fai_hub -> chain_hub. Vendor
security-hook tooling (FAI_BANNED_TERMS_FILE) + the .fai bundle ext left.
flutter analyze + test: clean (20 passed).

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/widgets/chain_flow_output.dart

@@ -0,0 +1,282 @@
+// ChainFlowOutput — type-aware renderer for one entry in
+// `runSavedFlow`'s output map. Reads `FlowOutput` and dispatches
+// to the right widget:
+//
+//   - text:    SelectableText for plain text; Markdown widget
+//              when the (hinted) MIME is text/markdown.
+//   - json:    indented JSON in a code-block container.
+//   - bytes:   inline image thumbnail when image/*, otherwise a
+//              "{mime}, {size}" summary. Always offers Save-as.
+//   - file:    "Open" button → SystemActions.openInOs(uri).
+//
+// Stateless on purpose: the dialog wraps it; we never own a
+// future or a controller here.
+
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:file_picker/file_picker.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
+
+import '../data/error_presentation.dart';
+import '../data/flow_output.dart';
+import '../data/format.dart';
+import '../data/system_actions.dart';
+import '../l10n/app_localizations.dart';
+import '../theme/theme.dart';
+import '../theme/tokens.dart';
+
+class ChainFlowOutput extends StatelessWidget {
+  final FlowOutput output;
+
+  const ChainFlowOutput({super.key, required this.output});
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    switch (output) {
+      case FlowOutputText(:final text):
+        return _TextView(text: text);
+      case FlowOutputJson(:final pretty):
+        return _CodeBlock(text: pretty, theme: theme);
+      case FlowOutputBytes(:final bytes, :final mimeType):
+        return _BytesView(bytes: bytes, mimeType: mimeType);
+      case FlowOutputFile(:final uri, :final mimeType):
+        return _FileView(uri: uri, mimeType: mimeType);
+      case FlowOutputUnknown():
+        return _CodeBlock(
+          text: AppLocalizations.of(context)!.flowsOutputUnknown,
+          theme: theme,
+        );
+    }
+  }
+}
+
+/// Plain-text renderer. Auto-detects markdown via a cheap
+/// heuristic (leading `#` heading, fenced code block, or
+/// numbered/bulleted list) so flows that emit text/markdown
+/// without setting an explicit MIME still render formatted.
+class _TextView extends StatelessWidget {
+  final String text;
+
+  const _TextView({required this.text});
+
+  static final RegExp _markdownHeuristic = RegExp(
+    r'(^|\n)(#{1,6}\s|```|\*\s|-\s|\d+\.\s)',
+  );
+
+  bool get _looksLikeMarkdown =>
+      text.length < 64 * 1024 && _markdownHeuristic.hasMatch(text);
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    if (_looksLikeMarkdown) {
+      return Container(
+        width: double.infinity,
+        padding: const EdgeInsets.all(ChainSpace.md),
+        decoration: BoxDecoration(
+          color: theme.colorScheme.surfaceContainerHigh,
+          borderRadius: BorderRadius.circular(ChainRadius.sm),
+          border: Border.all(color: theme.colorScheme.outlineVariant),
+        ),
+        child: MarkdownBody(
+          data: text,
+          selectable: true,
+          onTapLink: (_, href, _) async {
+            if (href != null && href.isNotEmpty) {
+              await SystemActions.openInOs(href);
+            }
+          },
+          styleSheet: ChainTheme.markdownStyle(theme),
+        ),
+      );
+    }
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.all(ChainSpace.md),
+      decoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+        borderRadius: BorderRadius.circular(ChainRadius.sm),
+        border: Border.all(color: theme.colorScheme.outlineVariant),
+      ),
+      child: SelectableText(
+        text,
+        style: theme.textTheme.bodyMedium?.copyWith(height: 1.5),
+      ),
+    );
+  }
+}
+
+class _CodeBlock extends StatelessWidget {
+  final String text;
+  final ThemeData theme;
+
+  const _CodeBlock({required this.text, required this.theme});
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.all(ChainSpace.md),
+      decoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+        borderRadius: BorderRadius.circular(ChainRadius.sm),
+        border: Border.all(color: theme.colorScheme.outlineVariant),
+      ),
+      child: SelectableText(
+        text,
+        style: ChainTheme.mono(size: 12, color: theme.colorScheme.onSurface),
+      ),
+    );
+  }
+}
+
+class _BytesView extends StatelessWidget {
+  final Uint8List bytes;
+  final String mimeType;
+
+  const _BytesView({required this.bytes, required this.mimeType});
+
+  bool get _isImage => mimeType.startsWith('image/');
+
+  /// Reasonable default filename for the Save dialog. Strips the
+  /// MIME up to the slash and uses the suffix when known
+  /// (image/png → output.png), otherwise a generic `.bin`.
+  String _defaultFilename() {
+    final slash = mimeType.indexOf('/');
+    if (slash < 0 || slash == mimeType.length - 1) return 'output.bin';
+    final sub = mimeType.substring(slash + 1);
+    // Strip common parameter suffixes (`png; charset=...`).
+    final semi = sub.indexOf(';');
+    final ext = semi < 0 ? sub : sub.substring(0, semi);
+    // `vnd.openxmlformats-…wordprocessingml.document` → docx.
+    if (ext.contains('wordprocessingml')) return 'output.docx';
+    if (ext.contains('spreadsheetml')) return 'output.xlsx';
+    if (ext.contains('presentationml')) return 'output.pptx';
+    return 'output.$ext';
+  }
+
+  Future<void> _save(BuildContext context) async {
+    final l = AppLocalizations.of(context)!;
+    final path = await FilePicker.saveFile(
+      dialogTitle: l.flowsOutputSaveAsTitle,
+      fileName: _defaultFilename(),
+    );
+    if (path == null) return;
+    try {
+      await File(path).writeAsBytes(bytes, flush: true);
+      if (!context.mounted) return;
+      ScaffoldMessenger.of(
+        context,
+      ).showSnackBar(SnackBar(content: Text(l.flowsOutputSavedAt(path))));
+    } catch (e) {
+      if (!context.mounted) return;
+      showFaiErrorSnack(context, 'flows.output.save', e);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.all(ChainSpace.md),
+      decoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+        borderRadius: BorderRadius.circular(ChainRadius.sm),
+        border: Border.all(color: theme.colorScheme.outlineVariant),
+      ),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          if (_isImage) ...[
+            ConstrainedBox(
+              constraints: const BoxConstraints(maxHeight: 240),
+              child: ClipRRect(
+                borderRadius: BorderRadius.circular(ChainRadius.sm),
+                child: Image.memory(bytes, fit: BoxFit.contain),
+              ),
+            ),
+            const SizedBox(height: ChainSpace.sm),
+          ],
+          Text(
+            '${mimeType.isEmpty ? l.flowsOutputBytesUnknownMime : mimeType}'
+            ' · ${humanBytes(bytes.length)}',
+            style: theme.textTheme.bodySmall?.copyWith(
+              color: theme.colorScheme.onSurfaceVariant,
+            ),
+          ),
+          const SizedBox(height: ChainSpace.sm),
+          OutlinedButton.icon(
+            icon: const Icon(Icons.save_alt, size: 16),
+            label: Text(l.flowsOutputSaveAs),
+            onPressed: () => _save(context),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+class _FileView extends StatelessWidget {
+  final String uri;
+  final String mimeType;
+
+  const _FileView({required this.uri, required this.mimeType});
+
+  Future<void> _open(BuildContext context) async {
+    // Most file-URIs come from modules that wrote a temp/output
+    // path on the host. SystemActions normalises `file://` for
+    // open-in-OS on all three platforms.
+    final target = uri.startsWith('file://') ? uri.substring(7) : uri;
+    final r = await SystemActions.openInOs(target);
+    if (!context.mounted || r.ok) return;
+    showFaiErrorSnack(
+      context,
+      'flows.output.open',
+      r.stderr.isEmpty ? 'open failed' : r.stderr,
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.all(ChainSpace.md),
+      decoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+        borderRadius: BorderRadius.circular(ChainRadius.sm),
+        border: Border.all(color: theme.colorScheme.outlineVariant),
+      ),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          SelectableText(
+            uri,
+            style: ChainTheme.mono(size: 11, color: theme.colorScheme.primary),
+          ),
+          if (mimeType.isNotEmpty) ...[
+            const SizedBox(height: 4),
+            Text(
+              mimeType,
+              style: theme.textTheme.bodySmall?.copyWith(
+                color: theme.colorScheme.onSurfaceVariant,
+              ),
+            ),
+          ],
+          const SizedBox(height: ChainSpace.sm),
+          OutlinedButton.icon(
+            icon: const Icon(Icons.open_in_new, size: 16),
+            label: Text(l.flowsOutputOpen),
+            onPressed: () => _open(context),
+          ),
+        ],
+      ),
+    );
+  }
+}