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/core/middleware.py

@@ -0,0 +1,37 @@
+"""CSRF middleware — Origin header validation for POST/PATCH/DELETE."""
+
+from __future__ import annotations
+
+from fastapi import Request, status
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import JSONResponse
+
+from app.config import get_settings
+
+
+class CSRFMiddleware(BaseHTTPMiddleware):
+    """Validate Origin header on all state-changing requests.
+    SameSite=Strict cookie + Origin validation = CSRF protection.
+    """
+
+    UNSAFE_METHODS = {"POST", "PATCH", "PUT", "DELETE"}
+
+    async def dispatch(self, request: Request, call_next):
+        if request.method in self.UNSAFE_METHODS:
+            origin = request.headers.get("origin")
+            if not origin:
+                return JSONResponse(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    content={"detail": "Missing Origin header", "code": "csrf_missing_origin"},
+                )
+
+            settings = get_settings()
+            allowed = settings.cors_origin_list
+            # In production, same-origin is enforced; in dev, explicit origins
+            if origin not in allowed:
+                return JSONResponse(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    content={"detail": "Invalid Origin", "code": "csrf_invalid_origin"},
+                )
+
+        return await call_next(request)