feat: Problems correlation fingerprint, count, last_seen (d1-2)

- Migration 003; windowed host+type+rule correlation on ingest

- GET /problems filters; GET /problems/{id} with event timeline; ack/resolve 409 guard

- Tests and SAC_PROBLEM_CORRELATION_WINDOW_MINUTES config

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/conftest.py

@@ -14,6 +14,7 @@ from sqlalchemy.orm import sessionmaker
 from sqlalchemy.pool import StaticPool
 
 from app.auth.api_key import hash_api_key
+from app.auth.jwt_auth import create_access_token
 from app.database import Base, get_db
 from app.main import app as fastapi_app
 import app.models  # noqa: F401 — register all tables on Base.metadata
@@ -80,3 +81,9 @@ def client(db_session, monkeypatch):
 @pytest.fixture
 def auth_headers():
     return {"Authorization": f"Bearer {TEST_API_KEY}"}
+
+
+@pytest.fixture
+def jwt_headers():
+    token = create_access_token("test-admin")
+    return {"Authorization": f"Bearer {token}"}