feat(studio): first-run UX, recovery affordances, l10n, bundled fonts

- Connection-aware Welcome: when the hub is down, show a hero with a
  primary "Start hub" CTA + install fallback instead of a dead,
  all-unchecked onboarding checklist (the first-run cliff).
- Actionable binary-not-found (file picker + install link, not a
  "set FAI_BIN" dead end) and a connect-failure banner after
  repeated failed health polls.
- Localize six hardcoded English error/toast clusters (DE+EN ARB).
- Bundle Inter + JetBrains Mono as assets; drop the runtime
  google_fonts fetch (air-gap / KRITIS safe, no font-swap flash).

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

pubspec.yaml

@@ -19,7 +19,6 @@ dependencies:
   # Sibling package; will move to Forgejo path once published.
   fai_client_sdk:
     path: ../fai_client_sdk_dart
-  google_fonts: ^8.1.0
   shared_preferences: ^2.5.5
   # Inline README rendering inside the Store detail sheet.
   # `flutter_markdown` is discontinued; `flutter_markdown_plus`
@@ -68,3 +67,24 @@ flutter:
   # Air-gap-friendly — no network calls to read these.
   assets:
     - assets/docs/
+  # Bundled fonts — Inter (UI) + JetBrains Mono (technical
+  # strings). Shipped as assets rather than fetched at runtime
+  # via google_fonts so the app works fully offline / air-gapped
+  # (KRITIS) and never shows a font-swap flash on first paint.
+  fonts:
+    - family: Inter
+      fonts:
+        - asset: assets/fonts/Inter-Regular.ttf
+          weight: 400
+        - asset: assets/fonts/Inter-Medium.ttf
+          weight: 500
+        - asset: assets/fonts/Inter-SemiBold.ttf
+          weight: 600
+        - asset: assets/fonts/Inter-Bold.ttf
+          weight: 700
+    - family: JetBrains Mono
+      fonts:
+        - asset: assets/fonts/JetBrainsMono-Regular.ttf
+          weight: 400
+        - asset: assets/fonts/JetBrainsMono-Medium.ttf
+          weight: 500