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/l10n/app_localizations_en.dart

@@ -1321,12 +1321,52 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Running $name';
   }
 
+  @override
+  String flowsResultTitle(String name) {
+    return '$name — result';
+  }
+
+  @override
+  String flowsErrorTitle(String name) {
+    return '$name — failed';
+  }
+
   @override
   String get flowsRunning => 'Flow running…';
 
   @override
   String get flowsNoOutputs => 'Flow completed with no declared outputs.';
 
+  @override
+  String get flowsOutputUnknown => 'Output payload variant not recognised.';
+
+  @override
+  String get flowsOutputBytesUnknownMime => 'binary';
+
+  @override
+  String get flowsOutputSaveAs => 'Save as…';
+
+  @override
+  String get flowsOutputSaveAsTitle => 'Save flow output';
+
+  @override
+  String flowsOutputSavedAt(String path) {
+    return 'Saved to $path';
+  }
+
+  @override
+  String flowsOutputSaveFailed(String error) {
+    return 'Save failed: $error';
+  }
+
+  @override
+  String get flowsOutputOpen => 'Open';
+
+  @override
+  String flowsOutputOpenFailed(String error) {
+    return 'Open failed: $error';
+  }
+
   @override
   String get approvalsTitle => 'Approvals';