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/theme/theme.dart

@@ -1,6 +1,7 @@
 // Theme assembly. ColorScheme + typography + component themes.
 
 import 'package:flutter/material.dart';
+import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:google_fonts/google_fonts.dart';
 
 import 'tokens.dart';
@@ -77,6 +78,69 @@ class FaiTheme {
         height: 1.4,
       );
 
+  /// Shared markdown style used by every inline doc renderer
+  /// (Welcome DocReaderSheet, Store module-detail DocsPanel,
+  /// future help surfaces). Centralising it means every doc
+  /// reads in the same typography, with the same dark-theme
+  /// safe colors.
+  ///
+  /// Why every property is set explicitly even when it just
+  /// re-states the default:
+  ///
+  /// - `flutter_markdown`'s `MarkdownStyleSheet.fromTheme(theme)`
+  ///   sets `code` with `backgroundColor: theme.cardTheme.color`.
+  ///   That per-span backgroundColor is rendered behind every
+  ///   character inside a fenced code block, which on a dark
+  ///   theme shows up as horizontal bands behind ASCII diagrams.
+  ///   We force `backgroundColor: Colors.transparent` to suppress
+  ///   it — the codeblock's own decoration provides the panel
+  ///   background.
+  /// - `blockquote` defaults to a hardcoded `Colors.blue.shade100`
+  ///   background that is unreadable in dark mode. We replace it
+  ///   with theme-aware tokens (surfaceContainer + left accent
+  ///   border).
+  /// - `tableCellsDecoration` has the same dark-mode bug, fixed
+  ///   the same way.
+  static MarkdownStyleSheet markdownStyle(ThemeData theme) {
+    return MarkdownStyleSheet.fromTheme(theme).copyWith(
+      p: theme.textTheme.bodyMedium?.copyWith(height: 1.5),
+      code: mono(
+        size: 12,
+        color: theme.colorScheme.onSurface,
+      ).copyWith(
+        backgroundColor: Colors.transparent,
+      ),
+      codeblockDecoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+        borderRadius: BorderRadius.circular(FaiRadius.sm),
+        border: Border.all(color: theme.colorScheme.outlineVariant),
+      ),
+      codeblockPadding: const EdgeInsets.all(FaiSpace.md),
+      blockquote: theme.textTheme.bodyMedium?.copyWith(
+        color: theme.colorScheme.onSurface,
+      ),
+      blockquoteDecoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainer,
+        borderRadius: BorderRadius.circular(FaiRadius.sm),
+        border: Border(
+          left: BorderSide(
+            color: theme.colorScheme.primary,
+            width: 3,
+          ),
+        ),
+      ),
+      blockquotePadding: const EdgeInsets.fromLTRB(
+        FaiSpace.md,
+        FaiSpace.sm,
+        FaiSpace.sm,
+        FaiSpace.sm,
+      ),
+      tableCellsDecoration: BoxDecoration(
+        color: theme.colorScheme.surfaceContainerHigh,
+      ),
+    );
+  }
+
   static ThemeData dark() {
     final scheme = ColorScheme(
       brightness: Brightness.dark,