feat(ks2): enable geocoding during reimport

Add geocode query param to /api/admin/reimport-ks2 (defaults true).
ks2.py passes ?geocode=true so postcodes are resolved to lat/lng in
the same migration pass.

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

backend/app.py

@@ -639,16 +639,18 @@ async def reload_data(
 @limiter.limit("2/minute")
 async def reimport_ks2(
     request: Request,
+    geocode: bool = True,
     _: 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.
+    Pass ?geocode=false to skip postcode → lat/lng resolution.
     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)
+    success = await loop.run_in_executor(None, lambda: run_full_migration(geocode=geocode))
     if not success:
         raise HTTPException(status_code=500, detail="Migration failed: no CSV data found in data directory")
     clear_cache()