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),
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}