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

frontend/src/hooks/useMapData.ts

@@ -7,6 +7,13 @@ import { fetchBansByCountry } from "../api/map";
 import type { BansByCountryResponse, MapBanItem, TimeRange } from "../types/map";
 import type { BanOriginFilter } from "../types/ban";
 
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+
+/** Debounce delay in milliseconds before firing a fetch after filter changes. */
+const DEBOUNCE_MS = 300;
+
 // ---------------------------------------------------------------------------
 // Return type
 // ---------------------------------------------------------------------------
@@ -40,30 +47,43 @@ export function useMapData(
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const abortRef = useRef<AbortController | null>(null);
+  const debounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   const load = useCallback((): void => {
-    abortRef.current?.abort();
-    abortRef.current = new AbortController();
+    // Cancel any pending debounce timer.
+    if (debounceRef.current != null) {
+      clearTimeout(debounceRef.current);
+    }
+    // Show loading immediately so the skeleton / spinner appears.
     setLoading(true);
     setError(null);
 
-    fetchBansByCountry(range, origin)
-      .then((resp) => {
-        setData(resp);
-      })
-      .catch((err: unknown) => {
-        if (err instanceof Error && err.name !== "AbortError") {
-          setError(err.message);
-        }
-      })
-      .finally((): void => {
-        setLoading(false);
-      });
+    debounceRef.current = setTimeout((): void => {
+      // Abort any in-flight request from a previous filter selection.
+      abortRef.current?.abort();
+      abortRef.current = new AbortController();
+
+      fetchBansByCountry(range, origin)
+        .then((resp) => {
+          setData(resp);
+        })
+        .catch((err: unknown) => {
+          if (err instanceof Error && err.name !== "AbortError") {
+            setError(err.message);
+          }
+        })
+        .finally((): void => {
+          setLoading(false);
+        });
+    }, DEBOUNCE_MS);
   }, [range, origin]);
 
   useEffect((): (() => void) => {
     load();
     return (): void => {
+      if (debounceRef.current != null) {
+        clearTimeout(debounceRef.current);
+      }
       abortRef.current?.abort();
     };
   }, [load]);