T01: core infrastructure + auth + multi-tenant + RLS

- 10 models: tenants, users, user_tenants, roles, sessions, audit_log, deletion_log, notifications, password_reset_tokens, api_tokens
- Session-based auth (Redis + PostgreSQL audit trail)
- Multi-tenant with ORM-level filtering + PostgreSQL RLS (set_config)
- RBAC with roles/permissions + field-level permissions
- CSRF protection via Origin header validation
- Auth rate limiting (Redis counters with TTL)
- CORS with explicit origins (no wildcard)
- Health endpoint (no auth required)
- Notification service + audit log middleware
- 29 tests, 26 ACs, all passing
- Coverage: 62% (infrastructure modules pending coverage in later tasks)

app/routes/health.py

@@ -0,0 +1,13 @@
+"""Health check endpoint."""
+
+from __future__ import annotations
+
+from fastapi import APIRouter
+
+router = APIRouter(tags=["health"])
+
+
+@router.get("/api/v1/health")
+async def health():
+    """Health check — no auth required."""
+    return {"status": "ok", "version": "1.0.0"}