feat: add Playwright configuration and initial e2e test for authentication

- Created Playwright configuration file to set up testing environment.
- Added a new e2e test for user authentication in login.spec.ts.
- Updated tsconfig.node.json to include playwright.config.ts.
- Enhanced vite.config.ts to include API proxying for backend integration.
- Added a placeholder for last run test results in .last-run.json.

backend/app/db/unit_of_work.py

@@ -0,0 +1,62 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Optional
+
+from sqlalchemy.orm import Session
+
+from backend.app.db.session import SessionLocal
+from backend.app.repositories import (
+    StationRepository,
+    TrainRepository,
+    TrainScheduleRepository,
+    TrackRepository,
+    UserRepository,
+)
+
+
+class SqlAlchemyUnitOfWork:
+    """Coordinate transactional work across repositories."""
+
+    def __init__(self, session_factory: Callable[[], Session] = SessionLocal) -> None:
+        self._session_factory = session_factory
+        self.session: Optional[Session] = None
+        self._committed = False
+        self.users: UserRepository
+        self.stations: StationRepository
+        self.tracks: TrackRepository
+        self.trains: TrainRepository
+        self.train_schedules: TrainScheduleRepository
+
+    def __enter__(self) -> "SqlAlchemyUnitOfWork":
+        self.session = self._session_factory()
+        self.users = UserRepository(self.session)
+        self.stations = StationRepository(self.session)
+        self.tracks = TrackRepository(self.session)
+        self.trains = TrainRepository(self.session)
+        self.train_schedules = TrainScheduleRepository(self.session)
+        return self
+
+    def __exit__(self, exc_type, exc, _tb) -> None:
+        try:
+            if exc:
+                self.rollback()
+            elif not self._committed:
+                self.commit()
+        finally:
+            if self.session is not None:
+                self.session.close()
+                self.session = None
+                self._committed = False
+
+    def commit(self) -> None:
+        if self.session is None:
+            raise RuntimeError("Unit of work is not active")
+        self.session.commit()
+        self._committed = True
+
+    def rollback(self) -> None:
+        if self.session is None:
+            return
+        self.session.rollback()
+        self._committed = False