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_en.arb

@@ -434,6 +434,22 @@
   "@flowsOpenInEditorFailed": {
     "placeholders": { "error": { "type": "String" } }
   },
+  "registryCredentialsHeader": "REGISTRY CREDENTIALS",
+  "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.",
+  "registryTokenStatusConfigured": "Configured ({chars} chars)",
+  "@registryTokenStatusConfigured": { "placeholders": { "chars": { "type": "int" } } },
+  "registryTokenStatusNotSet": "Not set",
+  "registryTokenFieldLabel": "Token",
+  "registryTokenFieldHint": "Paste your Forgejo or GitHub personal access token",
+  "registryTokenSaveButton": "Save",
+  "registryTokenClearButton": "Clear",
+  "registryTokenStorageHint": "Saved locally to ~/.fai/registry-token. Never sent to a remote service.",
+  "registryTokenSavedToast": "Registry token saved.",
+  "registryTokenClearedToast": "Registry token cleared.",
+  "registryTokenSaveFailedToast": "Could not save: {error}",
+  "@registryTokenSaveFailedToast": {
+    "placeholders": { "error": { "type": "String" } }
+  },
   "welcomeChecklistAllSetTitle": "You're set up.",
   "welcomeChecklistAllSetBody": "Three threads to pull on next:",
   "welcomeChecklistNextAuditTitle": "Read the audit log",