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/config.py

@@ -14,6 +14,7 @@ class Settings(BaseSettings):
     data_dir: Path = Field(default=Path("/data"), alias="DATA_DIR")
     database_url: str | None = Field(default=None, alias="DATABASE_URL")
     sync_interval_minutes: PositiveInt = Field(default=5, alias="SYNC_INTERVAL_MINUTES")
+    session_https_only: bool = Field(default=False, alias="SESSION_HTTPS_ONLY")
 
     @model_validator(mode="after")
     def derive_paths(self) -> "Settings":