fix(auth): store OAuth refresh token JTI to fix /auth/refresh after OAuth signup

OAuth callbacks (POST /auth/google/callback, POST /auth/microsoft/callback)
issued refresh tokens via create_refresh_token() but never persisted the JTI
in the refresh_tokens table. The /auth/refresh rotation logic does a
conditional UPDATE that requires a matching unrevoked row; without it the
first refresh attempt 401s with "Refresh token has been revoked" and OAuth
users get effectively logged out after the ~5 minute access-token expiry.

- Promote _store_refresh_token to module-public store_refresh_token in
  app.api.endpoints.auth (existing callers in /login, /login/json, /refresh
  updated in-place — same module, just renamed).
- OAuth callbacks now call store_refresh_token(...) + db.commit() after
  _sign_in_or_register returns. _sign_in_or_register already commits the
  user/account/identity rows; the refresh-token row gets its own commit.
- Tests:
  - test_oauth_google_callback_stores_refresh_token_jti — asserts the JTI
    hash is in refresh_tokens after a Google callback.
  - test_oauth_refresh_works_after_oauth_signup — full e2e: callback -> use
    returned refresh token at /auth/refresh -> 200 with rotated tokens.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/api/endpoints/auth.py

@@ -47,8 +47,16 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/auth", tags=["authentication"])
 
 
-async def _store_refresh_token(db: AsyncSession, refresh_token_str: str, user_id) -> None:
-    """Decode a refresh token JWT and store its hash in the database."""
+async def store_refresh_token(db: AsyncSession, refresh_token_str: str, user_id) -> None:
+    """Decode a refresh token JWT and store its hash in the database.
+
+    Module-public so OAuth callback endpoints (and any future token-issuing
+    surface) can register the JTI in the ``refresh_tokens`` table the same
+    way ``/auth/login`` does. Without this the first ``/auth/refresh`` call
+    will reject the token as "revoked" because no row exists.
+
+    Caller is responsible for committing the session.
+    """
     payload = decode_token(refresh_token_str)
     if payload and payload.get("jti"):
         token_record = RefreshToken(
@@ -320,7 +328,7 @@ async def login(
     refresh_token_str = create_refresh_token(data={"sub": str(user.id)})
 
     # Store refresh token hash in DB
-    await _store_refresh_token(db, refresh_token_str, user.id)
+    await store_refresh_token(db, refresh_token_str, user.id)
     await db.commit()
 
     return Token(
@@ -355,7 +363,7 @@ async def login_json(
     refresh_token_str = create_refresh_token(data={"sub": str(user.id)})
 
     # Store refresh token hash in DB
-    await _store_refresh_token(db, refresh_token_str, user.id)
+    await store_refresh_token(db, refresh_token_str, user.id)
     await db.commit()
 
     return Token(
@@ -413,7 +421,7 @@ async def refresh_token(
     new_refresh_token_str = create_refresh_token(data={"sub": str(user.id)})
 
     # Store new refresh token
-    await _store_refresh_token(db, new_refresh_token_str, user.id)
+    await store_refresh_token(db, new_refresh_token_str, user.id)
     await db.commit()
 
     return Token(