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/pages/audit.dart

@@ -973,7 +973,7 @@ class _ExplanationPanel extends StatelessWidget {
                     : theme.colorScheme.error,
               ),
             ),
-            if (result!.fixHint.isNotEmpty) ...[
+            if (result!.fixHint(l).isNotEmpty) ...[
               const SizedBox(height: FaiSpace.sm),
               Text(
                 l.auditFixLabel,
@@ -984,7 +984,7 @@ class _ExplanationPanel extends StatelessWidget {
               ),
               const SizedBox(height: 2),
               Text(
-                result!.fixHint,
+                result!.fixHint(l),
                 style: theme.textTheme.bodySmall?.copyWith(
                   color: theme.colorScheme.onSurface,
                 ),