feat(auth): restore Google sign-in and AI admin test routes

Google OAuth was implemented locally but never deployed; the login button
only renders when AUTH_GOOGLE_ID and AUTH_GOOGLE_SECRET are set. Also
restores /api/ai/test-* endpoints removed by mistake and wires Google
credentials into deploy workflows.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/locales/en.json

@@ -18,6 +18,7 @@
     "createAccount": "Create your account",
     "rememberMe": "Remember me",
     "orContinueWith": "Or continue with",
+    "continueWithGoogle": "Continue with Google",
     "checkYourEmail": "Check your email",
     "resetEmailSent": "We have sent a password reset link to your email address if it exists in our system.",
     "returnToLogin": "Return to Login",