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>

app/auth/csrf.py

@@ -14,5 +14,7 @@ def ensure_csrf_token(request: Request) -> str:
 
 def validate_csrf(request: Request, submitted_token: str) -> None:
     expected = request.session.get("csrf_token")
-    if not isinstance(expected, str) or not hmac.compare_digest(expected, submitted_token):
+    if not isinstance(expected, str) or not hmac.compare_digest(
+        expected.encode("utf-8"), submitted_token.encode("utf-8")
+    ):
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Invalid CSRF token")