fix: address final review findings for foundation plan

- C1: drop module-level app singleton in app/main.py so importing the
  package no longer validates Settings or creates DATA_DIR; run uvicorn
  with --factory in the Dockerfile. pytest now collects and passes with
  no ambient env vars.
- I2: add missing app/auth, app/security, app/web __init__.py so
  setuptools discovers all five packages.
- I3: resolve the Jinja2 template directory relative to __file__ instead
  of the process CWD.
- I4: add .gitignore covering .env, data/, .venv/, caches and build
  artifacts so example deployment secrets cannot be committed.
- I5: assert UserRepository.list_enabled() excludes disabled users.
- M6: encode both operands before hmac.compare_digest in validate_csrf so
  a non-ASCII token yields 403 instead of an unhandled 500.
- M9: remove unused relationship / HealthState imports.
- M11: make session cookie https_only configurable via SESSION_HTTPS_ONLY
  (default unchanged: false).
- M13: dispose SQLAlchemy engines in the db_session and client fixtures.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/conftest.py

@@ -22,8 +22,11 @@ def db_session() -> Session:
     )
     Base.metadata.create_all(engine)
     factory = sessionmaker(bind=engine, expire_on_commit=False)
-    with factory() as session:
-        yield session
+    try:
+        with factory() as session:
+            yield session
+    finally:
+        engine.dispose()
 
 
 @pytest.fixture
@@ -46,4 +49,8 @@ def client(tmp_path: Path) -> TestClient:
         DATABASE_URL=f"sqlite:///{tmp_path / 'app.db'}",
         SYNC_INTERVAL_MINUTES=5,
     )
-    return TestClient(create_app(settings))
+    app = create_app(settings)
+    try:
+        yield TestClient(app)
+    finally:
+        app.state.db_engine.dispose()