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/data/system_actions.dart

@@ -18,9 +18,61 @@
 
 import 'dart:io';
 
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// Sentinel returned in `_runFai(...).stderr` when no `fai`
+/// binary could be located. UI layers should not display this
+/// verbatim — they check [SystemActions.faiBinaryExists] first
+/// and render a localized, actionable message instead.
+const String kFaiBinaryNotFound = 'fai-binary-not-found';
+
+/// Getting-started / install guide for the F∆I platform. Opened
+/// in the OS browser as the fallback affordance when no `fai`
+/// binary can be located on the machine.
+const String kFaiInstallDocsUrl =
+    'https://git.flemming.ai/fai/platform#installation';
+
 class SystemActions {
   SystemActions._();
 
+  /// SharedPreferences key for an operator-chosen `fai` binary
+  /// path (set via the file picker when auto-detection fails).
+  static const String _kFaiBinaryPrefKey = 'system.fai_binary_path';
+
+  /// In-memory cache of the operator override, loaded once at
+  /// startup by [loadFaiBinaryOverride]. Null = no override.
+  static String? _faiBinaryOverride;
+
+  /// Restore the persisted `fai` binary override (if any) so it
+  /// is available before the first daemon action. Call once at
+  /// app start, alongside the other persisted-state loaders.
+  static Future<void> loadFaiBinaryOverride() async {
+    final prefs = await SharedPreferences.getInstance();
+    final p = prefs.getString(_kFaiBinaryPrefKey);
+    if (p != null && p.isNotEmpty && File(p).existsSync()) {
+      _faiBinaryOverride = p;
+    }
+  }
+
+  /// Persist an operator-chosen `fai` binary path. Used by the
+  /// "Locate `fai` binary…" affordance when auto-detection on
+  /// PATH and the canonical install dir both come up empty.
+  /// Returns false (and persists nothing) when [path] is empty
+  /// or does not point at an existing file.
+  static Future<bool> setFaiBinaryPath(String path) async {
+    if (path.isEmpty || !File(path).existsSync()) return false;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(_kFaiBinaryPrefKey, path);
+    _faiBinaryOverride = path;
+    return true;
+  }
+
+  /// True when a `fai` binary can be located (override, PATH, or
+  /// the canonical install dir). UI uses this to decide between
+  /// the normal daemon-control affordances and the "locate the
+  /// binary / read the install guide" recovery path.
+  static bool faiBinaryExists() => _faiExecutable() != null;
+
   /// Ask the OS to open [path] in the default handler. On macOS
   /// this opens text files in TextEdit, configs in the registered
   /// editor, etc. Returns true on a clean spawn (process exited
@@ -149,13 +201,11 @@ class SystemActions {
   ) async {
     final exe = _faiExecutable();
     if (exe == null) {
-      return (
-        ok: false,
-        stdout: '',
-        stderr:
-            'Could not locate the `fai` binary. Install via the '
-            'platform installer or set FAI_BIN to its full path.',
-      );
+      // Sentinel, not a user-facing string. Callers detect this
+      // via `faiBinaryExists()` and render a localized,
+      // actionable recovery message (locate binary / install
+      // guide) instead of CLI jargon like "set FAI_BIN".
+      return (ok: false, stdout: '', stderr: kFaiBinaryNotFound);
     }
     try {
       final r = await Process.run(exe, args);
@@ -175,9 +225,17 @@ class SystemActions {
     return (executable: 'xdg-open', args: const []);
   }
 
-  /// Locate the `fai` binary. Order: $FAI_BIN, PATH, fallback to
-  /// the canonical install location under the user's home dir.
+  /// Locate the `fai` binary. Order: operator override (set via
+  /// the file picker), $FAI_BIN, PATH, fallback to the canonical
+  /// install location under the user's home dir.
   static String? _faiExecutable() {
+    final override = _faiBinaryOverride;
+    if (override != null &&
+        override.isNotEmpty &&
+        File(override).existsSync()) {
+      return override;
+    }
+
     final fromEnv = Platform.environment['FAI_BIN'];
     if (fromEnv != null && fromEnv.isNotEmpty && File(fromEnv).existsSync()) {
       return fromEnv;