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/l10n/app_localizations_en.dart

@@ -2506,4 +2506,133 @@ class AppLocalizationsEn extends AppLocalizations {
   String installFailed(String error) {
     return 'Install failed: $error';
   }
+
+  @override
+  String get welcomeHubDownTitle => 'The hub isn\'t running yet';
+
+  @override
+  String get welcomeHubDownBody =>
+      'Studio talks to a local hub — the engine that loads modules and runs flows. It isn\'t reachable right now. Start it to begin.';
+
+  @override
+  String get welcomeHubDownStart => 'Start hub';
+
+  @override
+  String get welcomeHubDownStarting => 'Starting…';
+
+  @override
+  String get welcomeHubDownDocsLink =>
+      'Can\'t start it? Read the getting-started guide';
+
+  @override
+  String welcomeHubDownEndpoint(String endpoint) {
+    return 'Endpoint: $endpoint';
+  }
+
+  @override
+  String get daemonStartRequested => 'Daemon start requested. Reconnecting…';
+
+  @override
+  String daemonStartFailed(String detail) {
+    return 'Could not start daemon: $detail';
+  }
+
+  @override
+  String get faiBinaryNotFound =>
+      'Could not find the `fai` program on this machine.';
+
+  @override
+  String get faiBinaryNotFoundHint =>
+      'Install the F∆I platform, or point Studio at an existing `fai` binary.';
+
+  @override
+  String get faiBinaryLocateButton => 'Locate `fai` binary…';
+
+  @override
+  String get faiBinaryInstallDocsButton => 'Open install guide';
+
+  @override
+  String get faiBinaryPickerTitle => 'Select the `fai` binary';
+
+  @override
+  String faiBinarySetOk(String path) {
+    return 'Using `fai` binary at $path';
+  }
+
+  @override
+  String get sysAiFixParse =>
+      'The provider sent a response in an unexpected format. Providers that aren\'t OpenAI-compatible may need a translation proxy.';
+
+  @override
+  String sysAiFixUnknown(String kind) {
+    return 'Unexpected failure ($kind). See the System AI documentation.';
+  }
+
+  @override
+  String get sysAiFixDisabled =>
+      'Configure System AI in Settings (Cmd+,) → System AI panel.';
+
+  @override
+  String get sysAiFixEnvMissing =>
+      'The API-key environment variable is empty. Set it in your shell, then restart the daemon.';
+
+  @override
+  String get sysAiFixNetwork =>
+      'The hub can\'t reach the configured endpoint. Is your provider running?';
+
+  @override
+  String get sysAiFixHttp =>
+      'The provider returned a non-2xx status. Verify the endpoint, model name, and API key.';
+
+  @override
+  String get sysAiFixEmptyResponse =>
+      'The provider answered with no content. Try a different model or rephrase the prompt.';
+
+  @override
+  String channelSwitchOk(String name) {
+    return 'Switched active channel to \"$name\". Daemon restarted.';
+  }
+
+  @override
+  String channelSwitchFailed(String detail) {
+    return 'Channel switch failed: $detail';
+  }
+
+  @override
+  String get providerDescOllama =>
+      'Local `ollama serve`. Models stay on your machine. No API key needed.';
+
+  @override
+  String get providerDescOpenai =>
+      'OpenAI hosted API. Requires an API key. Data leaves your machine.';
+
+  @override
+  String get providerDescLmstudio =>
+      'Local LM Studio server. Models stay on your machine. No API key needed.';
+
+  @override
+  String get providerDescVllm =>
+      'Self-hosted vLLM or any other OpenAI-compatible server. Endpoint required.';
+
+  @override
+  String get providerDescCustom =>
+      'Anything else that speaks the OpenAI-compatible chat-completions wire (LiteLLM proxy, internal mirror, …).';
+
+  @override
+  String welcomeDocLoadFailedBody(
+    String slug,
+    String locale,
+    String attempted,
+    String underlying,
+  ) {
+    return 'Could not load the bundled doc \"$slug\" ($locale).\nTried: $attempted\nUnderlying: $underlying\nThis usually means the Studio build on disk predates the doc bundle. Rebuild Studio or open the online copy.';
+  }
+
+  @override
+  String hubUnreachableBanner(String endpoint) {
+    return 'Can\'t reach $endpoint — open Settings';
+  }
+
+  @override
+  String get hubUnreachableOpenSettings => 'Open Settings';
 }