feat: replace admin auth with cookie-based profile picker

Remove all authentication (login, sessions, bcrypt, itsdangerous) since
the app runs on a private homelab LAN. Replace with a profile picker
landing page and cookie-based profile selection (1-year expiry).

- Add Alembic migration to drop password_hash/is_admin columns
- Delete auth service, auth routes, login template, and auth tests
- Rewrite app/utils/auth.py with NoProfileSelectedError and
  require_active_profile dependency
- Add profile creation flow (GET/POST /profiles/create)
- Rewrite home page as profile picker with card layout
- Update all route files to use profile dependency instead of admin auth
- Remove bcrypt and itsdangerous from requirements
- Remove admin_username/admin_password from config
- Update all tests for new profile-based access model

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/conftest.py

@@ -11,8 +11,6 @@ from fastapi.testclient import TestClient
 def _set_test_env() -> None:
     """Ensure required env vars are set for all tests."""
     with patch.dict(os.environ, {
-        "ADMIN_USERNAME": "testadmin",
-        "ADMIN_PASSWORD": "testpass123",
         "APP_ENV": "development",
         "DATABASE_URL": "sqlite:///data/test_sneakyswole.db",
     }, clear=False):
@@ -26,3 +24,8 @@ def client() -> TestClient:
 
     app = create_app()
     return TestClient(app)
+
+
+def set_profile_cookie(client: TestClient, profile_id: int) -> None:
+    """Helper to set the active_profile_id cookie on a test client."""
+    client.cookies.set("active_profile_id", str(profile_id))