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_de.arb

@@ -506,8 +506,23 @@
   "flowsRunButton": "Starten",
   "flowsRunningTitle": "{name} läuft",
   "@flowsRunningTitle": { "placeholders": { "name": { "type": "String" } } },
+  "flowsResultTitle": "{name} — Ergebnis",
+  "@flowsResultTitle": { "placeholders": { "name": { "type": "String" } } },
+  "flowsErrorTitle": "{name} — fehlgeschlagen",
+  "@flowsErrorTitle": { "placeholders": { "name": { "type": "String" } } },
   "flowsRunning": "Flow läuft…",
   "flowsNoOutputs": "Flow abgeschlossen ohne deklarierte Outputs.",
+  "flowsOutputUnknown": "Unbekannter Output-Payload-Typ.",
+  "flowsOutputBytesUnknownMime": "Binärdaten",
+  "flowsOutputSaveAs": "Speichern unter…",
+  "flowsOutputSaveAsTitle": "Flow-Output speichern",
+  "flowsOutputSavedAt": "Gespeichert: {path}",
+  "@flowsOutputSavedAt": { "placeholders": { "path": { "type": "String" } } },
+  "flowsOutputSaveFailed": "Speichern fehlgeschlagen: {error}",
+  "@flowsOutputSaveFailed": { "placeholders": { "error": { "type": "String" } } },
+  "flowsOutputOpen": "Öffnen",
+  "flowsOutputOpenFailed": "Öffnen fehlgeschlagen: {error}",
+  "@flowsOutputOpenFailed": { "placeholders": { "error": { "type": "String" } } },
 
   "approvalsTitle": "Freigaben",
   "approvalsTabPending": "Offen",