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/widgets/fai_system_ai_editor.dart

@@ -86,6 +86,26 @@ class _ProviderPreset {
   static _ProviderPreset byWire(String wire) {
     return all.firstWhere((p) => p.wire == wire, orElse: () => all.first);
   }
+
+  /// Localized help body for this provider. Falls back to the
+  /// const English [description] for any future wire that has no
+  /// ARB key yet.
+  String descriptionFor(AppLocalizations l) {
+    switch (wire) {
+      case 'ollama':
+        return l.providerDescOllama;
+      case 'openai':
+        return l.providerDescOpenai;
+      case 'lmstudio':
+        return l.providerDescLmstudio;
+      case 'vllm':
+        return l.providerDescVllm;
+      case 'custom':
+        return l.providerDescCustom;
+      default:
+        return description;
+    }
+  }
 }
 
 class FaiSystemAiEditor extends StatefulWidget {
@@ -372,7 +392,7 @@ class _FaiSystemAiEditorState extends State<FaiSystemAiEditor> {
               _ProviderDropdown(value: _preset, onChanged: _onProviderChanged),
               const SizedBox(height: 4),
               Text(
-                _preset.description,
+                _preset.descriptionFor(l),
                 style: theme.textTheme.bodySmall?.copyWith(
                   color: theme.colorScheme.onSurfaceVariant,
                 ),
@@ -634,10 +654,10 @@ class _TestResultPanel extends StatelessWidget {
             ok ? l.systemAiReplyPrefix(result.text) : result.text,
             style: FaiTheme.mono(size: 11, color: theme.colorScheme.onSurface),
           ),
-          if (!ok && result.fixHint.isNotEmpty) ...[
+          if (!ok && result.fixHint(l).isNotEmpty) ...[
             const SizedBox(height: FaiSpace.xs),
             Text(
-              result.fixHint,
+              result.fixHint(l),
               style: theme.textTheme.bodySmall?.copyWith(
                 color: theme.colorScheme.onSurface,
               ),