feat(studio): registry credentials panel in Settings (v0.44.0)

The hub install path now reads `~/.fai/registry-token` as a
fallback when `FAI_REGISTRY_TOKEN` is unset (platform v0.10.92).
Studio now writes that file directly: a fresh operator pastes
the PAT into Settings → Registry credentials, hits Save, and
the next install attempt resolves the auth wall without any
shell or env-var setup.

The token never round-trips back into Studio after save —
status is shown only as "Configured (40 chars)" / "Not set"
with no display of the secret itself. The Clear action deletes
the file. On Unix the file is chmod-ed to 0600 (owner-only
read/write); Windows leaves the default user ACL in place.

Storage is strictly local: `~/.fai/registry-token`, never sent
to a remote service. The hint text under the field says so to
make the data flow explicit.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_localizations_en.dart

@@ -1131,6 +1131,49 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Could not open file: $error';
   }
 
+  @override
+  String get registryCredentialsHeader => 'REGISTRY CREDENTIALS';
+
+  @override
+  String get registryCredentialsBlurb =>
+      'Token used to download .fai modules from a registry behind a signin wall (Forgejo, GitHub-private). Stored at ~/.fai/registry-token, mode 0600. The FAI_REGISTRY_TOKEN env var still wins when set.';
+
+  @override
+  String registryTokenStatusConfigured(int chars) {
+    return 'Configured ($chars chars)';
+  }
+
+  @override
+  String get registryTokenStatusNotSet => 'Not set';
+
+  @override
+  String get registryTokenFieldLabel => 'Token';
+
+  @override
+  String get registryTokenFieldHint =>
+      'Paste your Forgejo or GitHub personal access token';
+
+  @override
+  String get registryTokenSaveButton => 'Save';
+
+  @override
+  String get registryTokenClearButton => 'Clear';
+
+  @override
+  String get registryTokenStorageHint =>
+      'Saved locally to ~/.fai/registry-token. Never sent to a remote service.';
+
+  @override
+  String get registryTokenSavedToast => 'Registry token saved.';
+
+  @override
+  String get registryTokenClearedToast => 'Registry token cleared.';
+
+  @override
+  String registryTokenSaveFailedToast(String error) {
+    return 'Could not save: $error';
+  }
+
   @override
   String get welcomeChecklistAllSetTitle => 'You\'re set up.';