feat(sprint18): editor autosave/reset, admin auth, QR reuse, Ed25519 prep

- Project editor: persist draft to localStorage, restore on reload,
  last-saved/draft-restored status indicators, section/whole-draft reset
  with confirmation.
- Extract shared QR/polling/expiry engine from TelegramLoginComponent
  (shared/qr-login) and reuse it for a new admin login flow.
- Admin authentication kept fully separate from customer session:
  own cookie/localStorage keys, signals, guard, and header interceptor
  (core/admin-auth).
- ?login=true / ?adminLogin=true open the respective login dialog for
  manual testing.
- Ed25519 challenge/verify interfaces (fail-closed no-op binding) ready
  for backend delivery.
- Document autosave/reset/admin-auth/QR-reuse/Ed25519 model and the
  remaining full-field-coverage gap in docs/Project-Editor.md.

src/app/i18n/en.ts

@@ -522,6 +522,13 @@ export const en: Translations = {
     promptImageUrl: 'Image URL',
     htmlEditorCode: 'Code',
     htmlEditorPreview: 'Preview',
+    lastSaved: 'Last saved',
+    draftRestored: 'A local draft was restored from your last session.',
+    dismiss: 'Dismiss',
+    resetDraft: 'Reset draft',
+    resetSection: 'Reset section',
+    confirmResetDraft: 'This discards all unpublished changes and restores the last published configuration. Continue?',
+    confirmResetSection: 'This discards unpublished changes in this section only. Continue?',
   },
   staticPages: {
     notFound: 'Page not found',
@@ -555,6 +562,16 @@ export const en: Translations = {
     qrExpired: 'QR code expired. Click to refresh',
     qrError: 'Could not create login session. Click to retry',
   },
+  adminAuth: {
+    loginRequired: 'Admin login required',
+    loginDescription: 'Log in with your admin account to continue. This is a separate session from the storefront login.',
+    checking: 'Checking...',
+    loginWithApp: 'Log in with app',
+    orScanQr: 'Or scan the QR code',
+    loginNote: 'You will be redirected back after login',
+    qrExpired: 'QR code expired. Click to refresh',
+    qrError: 'Could not create login session. Click to retry',
+  },
   ux: {
     items: 'items',
     wishlistTitle: 'Wishlist',