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/main.dart

@@ -35,6 +35,7 @@ Future<void> main() async {
   // (when installed) the operator's theme-plugin choice
   // before the first frame so nothing flickers on startup.
   await HubService.instance.loadPersistedEndpoint();
+  await SystemActions.loadFaiBinaryOverride();
   final themeMode = await HubService.instance.loadThemeMode();
   final locale = await HubService.instance.loadLocale();
   final themePlugin = await loadActiveThemePlugin();
@@ -245,6 +246,42 @@ class StudioShellState extends State<StudioShell> {
   String? _activeChannel; // local / dev / beta / production
   Timer? _healthPoll;
 
+  /// Consecutive failed health polls. After [_unreachableThreshold]
+  /// in a row we stop showing an indefinite silent "connecting…"
+  /// and surface a one-line "can't reach the hub" banner with a
+  /// jump to Settings.
+  int _failedPolls = 0;
+  static const int _unreachableThreshold = 3;
+
+  /// Whether to render the unreachable banner. Distinct from
+  /// `_connected == false` so a single transient miss doesn't
+  /// flash the banner — only sustained failure does.
+  bool get _hubUnreachable => _failedPolls >= _unreachableThreshold;
+
+  /// Current connection state, for descendants (e.g. WelcomePage)
+  /// that adapt their content to hub availability.
+  bool? get connected => _connected;
+
+  /// Start the local daemon via the platform binary, then surface
+  /// the outcome as a snackbar. Shared by the sidebar's connection
+  /// row and the WelcomePage hero CTA.
+  Future<void> startDaemon() async {
+    final l = AppLocalizations.of(context)!;
+    final r = await SystemActions.faiDaemon(['start']);
+    if (!mounted) return;
+    final detail = r.stderr.trim().isEmpty ? r.stdout.trim() : r.stderr.trim();
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(
+        content: Text(
+          r.ok ? l.daemonStartRequested : l.daemonStartFailed(detail),
+        ),
+      ),
+    );
+    // Probe again shortly so the UI flips to "connected" without
+    // waiting for the next 5 s tick.
+    Future.delayed(const Duration(seconds: 1), _checkHealth);
+  }
+
   /// Switch the sidebar's selected page by its registered id
   /// (`store`, `flows`, `audit`, etc.). Used by the welcome
   /// page's onboarding checklist to make each item a real
@@ -331,7 +368,17 @@ class StudioShellState extends State<StudioShell> {
   Future<void> _checkHealth() async {
     final ok = await HubService.instance.healthy();
     if (!mounted) return;
-    if (_connected != ok) setState(() => _connected = ok);
+    final wasUnreachable = _hubUnreachable;
+    final nextFailed = ok ? 0 : _failedPolls + 1;
+    final connectionChanged = _connected != ok;
+    final bannerChanged =
+        wasUnreachable != (nextFailed >= _unreachableThreshold);
+    if (connectionChanged || _failedPolls != nextFailed || bannerChanged) {
+      setState(() {
+        _connected = ok;
+        _failedPolls = nextFailed;
+      });
+    }
     if (ok) {
       try {
         final snap = await HubService.instance.channelStatus();
@@ -454,24 +501,35 @@ class StudioShellState extends State<StudioShell> {
                 ),
                 Container(width: 1, color: theme.colorScheme.outlineVariant),
                 Expanded(
-                  child: AnimatedSwitcher(
-                    duration: FaiMotion.base,
-                    switchInCurve: FaiMotion.easing,
-                    switchOutCurve: FaiMotion.easing,
-                    transitionBuilder: (child, anim) => FadeTransition(
-                      opacity: anim,
-                      child: SlideTransition(
-                        position: Tween<Offset>(
-                          begin: const Offset(0, 0.02),
-                          end: Offset.zero,
-                        ).animate(anim),
-                        child: child,
+                  child: Column(
+                    children: [
+                      if (_hubUnreachable)
+                        _HubUnreachableBanner(
+                          endpoint: HubService.instance.endpointLabel,
+                          onOpenSettings: () => FaiSettingsDialog.show(context),
+                        ),
+                      Expanded(
+                        child: AnimatedSwitcher(
+                          duration: FaiMotion.base,
+                          switchInCurve: FaiMotion.easing,
+                          switchOutCurve: FaiMotion.easing,
+                          transitionBuilder: (child, anim) => FadeTransition(
+                            opacity: anim,
+                            child: SlideTransition(
+                              position: Tween<Offset>(
+                                begin: const Offset(0, 0.02),
+                                end: Offset.zero,
+                              ).animate(anim),
+                              child: child,
+                            ),
+                          ),
+                          child: KeyedSubtree(
+                            key: ValueKey(_selectedIndex),
+                            child: _pages[_selectedIndex].page,
+                          ),
+                        ),
                       ),
-                    ),
-                    child: KeyedSubtree(
-                      key: ValueKey(_selectedIndex),
-                      child: _pages[_selectedIndex].page,
-                    ),
+                    ],
                   ),
                 ),
               ],
@@ -483,6 +541,58 @@ class StudioShellState extends State<StudioShell> {
   }
 }
 
+/// One-line banner shown when the hub has been unreachable for
+/// several consecutive health polls. Replaces the indefinite
+/// silent "connecting…" with an explicit message + a jump to
+/// Settings, where the operator can fix the endpoint.
+class _HubUnreachableBanner extends StatelessWidget {
+  final String endpoint;
+  final VoidCallback onOpenSettings;
+
+  const _HubUnreachableBanner({
+    required this.endpoint,
+    required this.onOpenSettings,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Material(
+      color: theme.colorScheme.errorContainer,
+      child: Padding(
+        padding: const EdgeInsets.symmetric(
+          horizontal: FaiSpace.lg,
+          vertical: FaiSpace.sm,
+        ),
+        child: Row(
+          children: [
+            Icon(
+              Icons.cloud_off_outlined,
+              size: 18,
+              color: theme.colorScheme.onErrorContainer,
+            ),
+            const SizedBox(width: FaiSpace.sm),
+            Expanded(
+              child: Text(
+                l.hubUnreachableBanner(endpoint),
+                style: theme.textTheme.bodySmall?.copyWith(
+                  color: theme.colorScheme.onErrorContainer,
+                ),
+              ),
+            ),
+            const SizedBox(width: FaiSpace.sm),
+            TextButton(
+              onPressed: onOpenSettings,
+              child: Text(l.hubUnreachableOpenSettings),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
 /// Intents driven by the Shortcuts/Actions pair on the shell.
 class _GoToPageIntent extends Intent {
   final int index;
@@ -553,7 +663,12 @@ class _SidebarState extends State<_Sidebar>
     super.initState();
     _ctrl = AnimationController(
       vsync: this,
-      duration: FaiMotion.fast,
+      // Expand uses the slow (~320 ms) token: the icon→label
+      // reveal is a deliberate, eased gesture, not a flicker.
+      // The collapse runs faster (reverseDuration) so dismissing
+      // the rail feels crisp rather than sluggish.
+      duration: FaiMotion.slow,
+      reverseDuration: FaiMotion.base,
       value: 0,
     );
   }
@@ -565,14 +680,14 @@ class _SidebarState extends State<_Sidebar>
   }
 
   Future<void> _startDaemon(BuildContext context) async {
+    final l = AppLocalizations.of(context)!;
     final r = await SystemActions.faiDaemon(['start']);
     if (!context.mounted) return;
+    final detail = r.stderr.trim().isEmpty ? r.stdout.trim() : r.stderr.trim();
     ScaffoldMessenger.of(context).showSnackBar(
       SnackBar(
         content: Text(
-          r.ok
-              ? 'Daemon start requested. Reconnecting…'
-              : 'Could not start daemon: ${r.stderr.trim().isEmpty ? r.stdout.trim() : r.stderr.trim()}',
+          r.ok ? l.daemonStartRequested : l.daemonStartFailed(detail),
         ),
       ),
     );
@@ -1161,7 +1276,16 @@ class _SidebarItemState extends State<_SidebarItem> {
             // the left. The bg highlight spans the rail's
             // current width (typical nav-rail behaviour).
             padding: const EdgeInsets.symmetric(vertical: FaiSpace.md),
-            decoration: BoxDecoration(color: bg),
+            decoration: BoxDecoration(
+              color: bg,
+              borderRadius: BorderRadius.circular(FaiRadius.sm),
+              // Lift only the selected item — a whisper of depth
+              // marks "you are here" without competing with the
+              // accent fill.
+              boxShadow: widget.selected
+                  ? FaiElevation.low(theme.brightness)
+                  : null,
+            ),
             child: content,
           ),
         ),