Optimise geo lookup and aggregation for 10k+ IPs

- Add persistent geo_cache SQLite table (db.py)
- Rewrite geo_service: batch API (100 IPs/call), two-tier cache,
  no caching of failed lookups so they are retried
- Pre-warm geo cache from DB on startup (main.py lifespan)
- Rewrite bans_by_country: SQL GROUP BY ip aggregation + lookup_batch
  instead of 2000-row fetch + asyncio.gather individual calls
- Pre-warm geo cache after blocklist import (blocklist_service)
- Add 300ms debounce to useMapData hook to cancel stale requests
- Add perf benchmark asserting <2s for 10k bans
- Add seed_10k_bans.py script for manual perf testing

backend/app/main.py

@@ -134,6 +134,11 @@ async def _lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     http_session: aiohttp.ClientSession = aiohttp.ClientSession()
     app.state.http_session = http_session
 
+    # --- Pre-warm geo cache from the persistent store ---
+    from app.services import geo_service  # noqa: PLC0415
+
+    await geo_service.load_cache_from_db(db)
+
     # --- Background task scheduler ---
     scheduler: AsyncIOScheduler = AsyncIOScheduler(timezone="UTC")
     scheduler.start()