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>

lib/theme/theme.dart

@@ -2,55 +2,75 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
-import 'package:google_fonts/google_fonts.dart';
 
 import 'tokens.dart';
 
 class FaiTheme {
   FaiTheme._();
 
+  /// Bundled font families. Declared in pubspec.yaml `fonts:` and
+  /// shipped as TTF assets under `assets/fonts/` — NOT fetched at
+  /// runtime via google_fonts. This keeps the app working fully
+  /// offline / air-gapped (KRITIS) and avoids the font-swap flash
+  /// google_fonts shows on first paint.
+  static const String _uiFamily = 'Inter';
+  static const String _monoFamily = 'JetBrains Mono';
+
   /// Inter for UI, JetBrains Mono for technical strings (IDs,
-  /// paths, capability refs). Both via google_fonts so they
-  /// bundle on first run; for production we'd ship them as
-  /// app assets.
+  /// paths, capability refs). Both bundled (see [_uiFamily]).
   static TextTheme _textTheme(Brightness b) {
     final base = b == Brightness.dark
         ? Typography.whiteCupertino
         : Typography.blackCupertino;
-    return GoogleFonts.interTextTheme(base).copyWith(
-      displaySmall: GoogleFonts.inter(
+    return base.apply(fontFamily: _uiFamily).copyWith(
+      displaySmall: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 28,
         fontWeight: FontWeight.w600,
         letterSpacing: -0.4,
       ),
-      headlineSmall: GoogleFonts.inter(
+      headlineSmall: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 20,
         fontWeight: FontWeight.w600,
         letterSpacing: -0.2,
       ),
-      titleMedium: GoogleFonts.inter(
+      titleMedium: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 15,
         fontWeight: FontWeight.w600,
         letterSpacing: 0,
       ),
-      titleSmall: GoogleFonts.inter(fontSize: 13, fontWeight: FontWeight.w500),
-      bodyLarge: GoogleFonts.inter(
+      titleSmall: const TextStyle(
+        fontFamily: _uiFamily,
+        fontSize: 13,
+        fontWeight: FontWeight.w500,
+      ),
+      bodyLarge: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 14,
         fontWeight: FontWeight.w400,
         height: 1.45,
       ),
-      bodyMedium: GoogleFonts.inter(
+      bodyMedium: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 13,
         fontWeight: FontWeight.w400,
         height: 1.4,
       ),
-      bodySmall: GoogleFonts.inter(
+      bodySmall: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 12,
         fontWeight: FontWeight.w400,
         height: 1.4,
       ),
-      labelMedium: GoogleFonts.inter(fontSize: 12, fontWeight: FontWeight.w500),
-      labelSmall: GoogleFonts.inter(
+      labelMedium: const TextStyle(
+        fontFamily: _uiFamily,
+        fontSize: 12,
+        fontWeight: FontWeight.w500,
+      ),
+      labelSmall: const TextStyle(
+        fontFamily: _uiFamily,
         fontSize: 11,
         fontWeight: FontWeight.w500,
         letterSpacing: 0.2,
@@ -59,12 +79,14 @@ class FaiTheme {
   }
 
   /// JetBrains Mono for monospaced technical content. Used by
-  /// FaiMono helper.
+  /// FaiMono helper. Only Regular (400) and Medium (500) weights
+  /// are bundled — heavier requests fall back to the nearest.
   static TextStyle mono({
     double size = 12,
     FontWeight weight = FontWeight.w400,
     Color? color,
-  }) => GoogleFonts.jetBrainsMono(
+  }) => TextStyle(
+    fontFamily: _monoFamily,
     fontSize: size,
     fontWeight: weight,
     color: color,
@@ -221,8 +243,8 @@ class FaiTheme {
         scrolledUnderElevation: 0,
         centerTitle: false,
         // Bake the foreground colour straight into the title
-        // style. `headlineSmall` is built from GoogleFonts.inter
-        // with no color slot, and Material's "merge foreground
+        // style. `headlineSmall` is built from the bundled Inter
+        // family with no color slot, and Material's "merge foreground
         // colour at draw time" path leaves it null in some
         // light-mode builds — the title rendered white-on-white.
         titleTextStyle: textTheme.headlineSmall?.copyWith(