feat: Task 4 — paginated banned-IPs section on jail detail page

Backend:
- Add JailBannedIpsResponse Pydantic model (ban.py)
- Add get_jail_banned_ips() service: server-side pagination, optional
  IP substring search, geo enrichment on page slice only (jail_service.py)
- Add GET /api/jails/{name}/banned endpoint with page/page_size/search
  query params, 400/404/502 error handling (routers/jails.py)
- 23 new tests: 13 service tests + 10 router tests (all passing)

Frontend:
- Add JailBannedIpsResponse TS interface (types/jail.ts)
- Add jailBanned endpoint helper (api/endpoints.ts)
- Add fetchJailBannedIps() API function (api/jails.ts)
- Add BannedIpsSection component: Fluent UI DataGrid, debounced search
  (300 ms), prev/next pagination, page-size dropdown, per-row unban
  button, loading spinner, empty state, error MessageBar (BannedIpsSection.tsx)
- Mount BannedIpsSection in JailDetailPage between stats and patterns
- 12 new Vitest tests for BannedIpsSection (all passing)

frontend/src/pages/JailDetailPage.tsx

@@ -41,6 +41,7 @@ import {
 import { useJailDetail } from "../hooks/useJails";
 import type { Jail } from "../types/jail";
 import { ApiError } from "../api/client";
+import { BannedIpsSection } from "../components/jail/BannedIpsSection";
 
 // ---------------------------------------------------------------------------
 // Styles
@@ -624,6 +625,7 @@ export function JailDetailPage(): React.JSX.Element {
       </div>
 
       <JailInfoSection jail={jail} onRefresh={refresh} />
+      <BannedIpsSection jailName={name} />
       <PatternsSection jail={jail} />
       <BantimeEscalationSection jail={jail} />
       <IgnoreListSection