feat(integrator): add KS2 re-import via Kestra and backend admin endpoint

- backend: POST /api/admin/reimport-ks2 runs full CSV migration in a thread
- backend/docker-compose: ADMIN_API_KEY env var (default: changeme) so the
  key is stable across restarts and the integrator can call the endpoint
- integrator: sources/ks2.py triggers the backend endpoint (900s timeout)
- integrator: flows/ks2.yml Kestra flow (manual trigger, no schedule)

To re-ingest after a DB wipe: trigger the ks2-reimport flow from the
Kestra UI at http://localhost:8080.

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

integrator/scripts/config.py

@@ -9,3 +9,6 @@ DATABASE_URL = os.environ.get(
 
 DATA_DIR = Path(os.environ.get("DATA_DIR", "/data"))
 SUPPLEMENTARY_DIR = DATA_DIR / "supplementary"
+
+BACKEND_URL = os.environ.get("BACKEND_URL", "http://backend:80")
+ADMIN_API_KEY = os.environ.get("ADMIN_API_KEY", "changeme")