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_binary_recovery.dart

@@ -0,0 +1,95 @@
+// Recovery affordance shown when Studio cannot locate the `fai`
+// binary on the machine. Replaces the old CLI-jargon dead-end
+// ("set FAI_BIN to its full path") with two acts a non-CLI
+// operator can actually take:
+//
+//   1. Locate the binary with a native file picker, persisting
+//      the choice via SystemActions.setFaiBinaryPath.
+//   2. Open the install guide in the OS browser.
+
+import 'package:file_picker/file_picker.dart';
+import 'package:flutter/material.dart';
+
+import '../data/system_actions.dart';
+import '../l10n/app_localizations.dart';
+import '../theme/tokens.dart';
+
+class FaiBinaryRecovery extends StatelessWidget {
+  /// Fired after the operator successfully picks a `fai` binary,
+  /// so the host can retry whatever action hit the missing
+  /// binary (e.g. re-run the daemon start / status probe).
+  final VoidCallback? onLocated;
+
+  const FaiBinaryRecovery({super.key, this.onLocated});
+
+  Future<void> _locate(BuildContext context) async {
+    final l = AppLocalizations.of(context)!;
+    final messenger = ScaffoldMessenger.of(context);
+    final picked = await FilePicker.pickFiles(
+      dialogTitle: l.faiBinaryPickerTitle,
+    );
+    final path = picked?.files.single.path;
+    if (path == null) return;
+    final ok = await SystemActions.setFaiBinaryPath(path);
+    messenger.showSnackBar(
+      SnackBar(
+        content: Text(ok ? l.faiBinarySetOk(path) : l.faiBinaryNotFound),
+      ),
+    );
+    if (ok) onLocated?.call();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.all(FaiSpace.md),
+      decoration: BoxDecoration(
+        color: theme.colorScheme.errorContainer.withValues(alpha: 0.4),
+        borderRadius: BorderRadius.circular(FaiRadius.sm),
+        border: Border.all(
+          color: theme.colorScheme.error.withValues(alpha: 0.4),
+        ),
+      ),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Text(
+            l.faiBinaryNotFound,
+            style: theme.textTheme.bodyMedium?.copyWith(
+              fontWeight: FontWeight.w600,
+              color: theme.colorScheme.error,
+            ),
+          ),
+          const SizedBox(height: FaiSpace.xs),
+          Text(
+            l.faiBinaryNotFoundHint,
+            style: theme.textTheme.bodySmall?.copyWith(
+              color: theme.colorScheme.onSurfaceVariant,
+            ),
+          ),
+          const SizedBox(height: FaiSpace.md),
+          Wrap(
+            spacing: FaiSpace.sm,
+            runSpacing: FaiSpace.sm,
+            children: [
+              FilledButton.tonalIcon(
+                onPressed: () => _locate(context),
+                icon: const Icon(Icons.folder_open, size: 16),
+                label: Text(l.faiBinaryLocateButton),
+              ),
+              OutlinedButton.icon(
+                onPressed: () =>
+                    SystemActions.openInOs(kFaiInstallDocsUrl),
+                icon: const Icon(Icons.open_in_new, size: 16),
+                label: Text(l.faiBinaryInstallDocsButton),
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}

lib/widgets/fai_settings_dialog.dart

@@ -293,11 +293,12 @@ class _FaiSettingsDialogState extends State<FaiSettingsDialog> {
     });
     final r = await SystemActions.faiChannelSwitch(name);
     if (!mounted) return;
+    final l = AppLocalizations.of(context)!;
     setState(() {
       _saving = false;
       _channelToast = r.ok
-          ? 'Switched active channel to "$name". Daemon restarted.\n${r.stdout.trim()}'
-          : 'Channel switch failed: ${r.stderr.isEmpty ? r.stdout : r.stderr}';
+          ? '${l.channelSwitchOk(name)}\n${r.stdout.trim()}'
+          : l.channelSwitchFailed(r.stderr.isEmpty ? r.stdout : r.stderr);
     });
     if (r.ok) await _loadChannels();
   }

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,
               ),

lib/widgets/widgets.dart

@@ -4,6 +4,7 @@
 // primitives directly — no Material `Card` / generic `Container`
 // soup in page code.
 
+export 'fai_binary_recovery.dart';
 export 'fai_card.dart';
 export 'fai_data_row.dart';
 export 'fai_delta_mark.dart';