feat(studio): typed flow outputs + on-disk docs + UX polish

Documentation system (the original "whole docs system is broken"
complaint):
- Studio reads inline docs from disk via the new
  getInstalledModuleDocs RPC. No network, no auth, no provider
  lock-in.
- store.dart probes for MODULE.md eagerly when a module-detail
  sheet opens (a single file stat). The Documentation section
  only renders when the bundle actually shipped docs.
- Shared FaiTheme.markdownStyle helper used by Welcome's
  DocReaderSheet and Store's DocsPanel so every inline doc
  reads in the same typography. The shared style forces
  code.backgroundColor = transparent to suppress the per-span
  bands flutter_markdown's default code style draws on dark
  themes.

Flow run dialog:
- Run-button gating now strips the @version suffix from
  installed capabilities before the contains() check. Without
  this fix the button stayed disabled for every flow with
  dependencies, even after a successful install.
- Studio derives a MIME type from the picked file's extension
  (small per-suffix map; .pdf, .docx, .txt, .json, ...) and
  forwards it to the hub. Fixes "unsupported MIME type:
  application/octet-stream" from text.extract.
- Dialog title tracks the future's state: running -> "extract
  laeuft", success -> "extract -- Ergebnis", failure ->
  "extract -- fehlgeschlagen".
- Output rendering moved from String stringification to a
  sealed FlowOutput type (Text / Json / Bytes / File / Unknown).
  A new FaiFlowOutput widget dispatches per variant: markdown
  for text/markdown (heuristic), pretty JSON for proto Struct,
  inline image preview + Save-As for bytes, Open for file URIs.

Byte sizes:
- New humanBytes() helper renders 23.3 kB / 1.04 MB style values
  with three significant digits, matching Finder / GNOME Files.
  Wired into flow-card pills, picked-file readouts, and the
  bytes-payload preview line.

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

lib/data/hub.dart

@@ -11,6 +11,9 @@ import 'package:fai_dart_sdk/fai_dart_sdk.dart';
 import 'package:flutter/widgets.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
+import 'flow_output.dart';
+export 'flow_output.dart';
+
 class HubService {
   HubService._();
   static final HubService instance = HubService._();
@@ -346,17 +349,26 @@ class HubService {
     return (name: r.name, version: r.version);
   }
 
-  /// Fetch a module's README markdown via the hub. Errors come
-  /// back as `errorKind` strings (not exceptions) so callers can
-  /// render fallback UI without try/catch ceremony.
-  Future<({String errorKind, String text, String sourceUrl})>
-      fetchModuleDocs(String name, {String locale = ''}) async {
-    final r = await _client.fetchModuleDocs(name, locale: locale);
-    return (
-      errorKind: r.errorKind,
-      text: r.text,
-      sourceUrl: r.sourceUrl,
-    );
+  /// Read the installed module's `MODULE.md` (or
+  /// `MODULE.<locale>.md`) from disk under
+  /// `~/.fai/modules/<module>/`. Air-gap friendly, no network.
+  ///
+  /// `state` is one of:
+  ///   - `'found'`     — `text` holds the markdown
+  ///   - `'no_docs'`   — module installed but bundle had no docs
+  ///   - `'not_installed'` — module isn't installed at all
+  Future<({String state, String text, String sourcePath})>
+      readInstalledModuleDocs(String name, {String locale = ''}) async {
+    final r = await _client.getInstalledModuleDocs(name, locale: locale);
+    final String state;
+    if (r.notInstalled) {
+      state = 'not_installed';
+    } else if (r.text.isEmpty) {
+      state = 'no_docs';
+    } else {
+      state = 'found';
+    }
+    return (state: state, text: r.text, sourcePath: r.sourcePath);
   }
 
   /// Snapshot of every configured MCP server.
@@ -560,35 +572,31 @@ class HubService {
   /// land as text Payloads, byte values as bytes Payloads —
   /// flows that mix both (e.g. extract taking a `document:
   /// bytes` plus a text-shaped option) flow through one RPC.
-  /// Returns the named outputs as a map of UI-friendly strings.
-  Future<Map<String, String>> runSavedFlow({
+  /// [fileMimeTypes] is keyed the same as [fileInputs]; missing
+  /// entries fall back to `application/octet-stream`. Modules
+  /// often gate on MIME (the `text.extract` module refuses
+  /// octet-stream), so callers should provide a real type.
+  /// Returns the named outputs as a map of typed [FlowOutput]
+  /// values so each page can render text / JSON / bytes / file
+  /// with the right widget.
+  Future<Map<String, FlowOutput>> runSavedFlow({
     required String name,
     Map<String, String> textInputs = const {},
     Map<String, Uint8List> fileInputs = const {},
+    Map<String, String> fileMimeTypes = const {},
   }) async {
     final r = await _client.runSavedFlow(
       name: name,
       textInputs: textInputs,
       fileInputs: fileInputs,
+      fileMimeTypes: fileMimeTypes,
     );
     return {
       for (final entry in r.outputs.entries)
-        entry.key: _payloadToText(entry.value),
+        entry.key: FlowOutput.fromPayload(entry.value),
     };
   }
 
-  String _payloadToText(Payload p) {
-    if (p.hasText()) return p.text;
-    if (p.hasJson()) return p.json.toString();
-    if (p.hasBytes()) {
-      return '<bytes: ${p.bytes.data.length} bytes, ${p.bytes.mimeType}>';
-    }
-    if (p.hasFile()) {
-      return '<file: ${p.file.uri}>';
-    }
-    return '<unknown payload variant>';
-  }
-
   Future<List<AuditEvent>> recentEvents({
     int limit = 50,
     List<String> types = const [],