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>

backend/app.py

@@ -19,6 +19,7 @@ from slowapi.util import get_remote_address
 from slowapi.errors import RateLimitExceeded
 from starlette.middleware.base import BaseHTTPMiddleware
 
+import asyncio
 from .config import settings
 from .data_loader import (
     clear_cache,
@@ -28,6 +29,7 @@ from .data_loader import (
 )
 from .data_loader import get_data_info as get_db_info
 from .database import check_and_migrate_if_needed
+from .migration import run_full_migration
 from .schemas import METRIC_DEFINITIONS, RANKING_COLUMNS, SCHOOL_COLUMNS
 from .utils import clean_for_json
 
@@ -633,6 +635,27 @@ async def reload_data(
     return {"status": "reloaded"}
 
 
+@app.post("/api/admin/reimport-ks2")
+@limiter.limit("2/minute")
+async def reimport_ks2(
+    request: Request,
+    _: bool = Depends(verify_admin_api_key)
+):
+    """
+    Re-run the full KS2 CSV migration (drop + reimport schools and results).
+    Use when the database has been wiped and needs repopulating from the CSV files.
+    Runs synchronously — expect this to take several minutes.
+    Requires X-API-Key header with valid admin API key.
+    """
+    loop = asyncio.get_event_loop()
+    success = await loop.run_in_executor(None, run_full_migration)
+    if not success:
+        raise HTTPException(status_code=500, detail="Migration failed: no CSV data found in data directory")
+    clear_cache()
+    load_school_data()
+    return {"status": "reimported"}
+
+
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