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_de.arb

@@ -433,6 +433,22 @@
   "@flowsOpenInEditorFailed": {
     "placeholders": { "error": { "type": "String" } }
   },
+  "registryCredentialsHeader": "REGISTRY-ZUGANGSDATEN",
+  "registryCredentialsBlurb": "Token zum Herunterladen von .fai-Modulen aus einer Registry mit Anmeldepflicht (Forgejo, private GitHub-Repos). Gespeichert in ~/.fai/registry-token, Modus 0600. Die Umgebungsvariable FAI_REGISTRY_TOKEN hat weiterhin Vorrang, wenn gesetzt.",
+  "registryTokenStatusConfigured": "Konfiguriert ({chars} Zeichen)",
+  "@registryTokenStatusConfigured": { "placeholders": { "chars": { "type": "int" } } },
+  "registryTokenStatusNotSet": "Nicht gesetzt",
+  "registryTokenFieldLabel": "Token",
+  "registryTokenFieldHint": "Forgejo- oder GitHub-PAT einfügen",
+  "registryTokenSaveButton": "Speichern",
+  "registryTokenClearButton": "Entfernen",
+  "registryTokenStorageHint": "Lokal gespeichert in ~/.fai/registry-token. Wird nie an einen Remote-Dienst übertragen.",
+  "registryTokenSavedToast": "Registry-Token gespeichert.",
+  "registryTokenClearedToast": "Registry-Token entfernt.",
+  "registryTokenSaveFailedToast": "Speichern fehlgeschlagen: {error}",
+  "@registryTokenSaveFailedToast": {
+    "placeholders": { "error": { "type": "String" } }
+  },
   "welcomeChecklistAllSetTitle": "Du bist eingerichtet.",
   "welcomeChecklistAllSetBody": "Drei Stränge, an denen du als nächstes ziehen kannst:",
   "welcomeChecklistNextAuditTitle": "Audit-Log lesen",