agent-rls: PostgreSQL Row Level Security für Mandanten-Isolation

- Migration 0024: RLS + FORCE RLS auf 18 Tabellen
  - Direkte company_id-Policies: users, departments, companies, absence_types,
    audit_logs, kiosk_devices, ldap_configs, smtp_configs, caldav_company_configs,
    work_schedules, overtime_balances
  - JOIN-Policies (user_id → company_id): absences, sessions, password_resets,
    time_entries, vacation_balances, caldav_user_configs
  - public_holidays ausgenommen (globale Referenztabelle)
- database.py: get_db setzt bypass_rls='on' als Default (Auth-Endpoints unverändert)
- dependencies.py: get_current_user setzt app.company_id + bypass_rls='off'
  für alle nicht-SUPER_ADMIN Rollen
- migrations/env.py: Alembic-Migrationen nutzen bypass_rls='on'
- tests/conftest.py: override_get_db setzt bypass_rls='on' für Test-Session

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

backend/tests/conftest.py

@@ -43,6 +43,10 @@ async def db_session():
 async def client(db_session: AsyncSession):
     async def override_get_db():
         try:
+            # Tests use a shared session without a real transaction context per
+            # request. Set bypass_rls = 'on' so that all test queries succeed
+            # regardless of whether app.company_id is set.
+            await db_session.execute(text("SET LOCAL app.bypass_rls = 'on'"))
             yield db_session
             await db_session.commit()
         except Exception: