Stage 7: configuration view — backend service, routers, tests, and frontend

- config_service.py: read/write jail config via asyncio.gather, global
  settings, in-process regex validation, log preview via _read_tail_lines
- server_service.py: read/write server settings, flush logs
- config router: 9 endpoints for jail/global config, regex-test,
  logpath management, log preview
- server router: GET/PUT settings, POST flush-logs
- models/config.py expanded with JailConfig, GlobalConfigUpdate,
  LogPreview* models
- 285 tests pass (68 new), ruff clean, mypy clean (44 files)
- Frontend: types/config.ts, api/config.ts, hooks/useConfig.ts,
  ConfigPage.tsx full implementation (Jails accordion editor,
  Global config, Server settings, Regex Tester with preview)
- Fixed pre-existing frontend lint: JSX.Element → React.JSX.Element
  (10 files), void/promise patterns in useServerStatus + useJails,
  no-misused-spread in client.ts, eslint.config.ts self-excluded

frontend/src/hooks/useServerStatus.ts

@@ -36,7 +36,7 @@ export function useServerStatus(): UseServerStatusResult {
   const [error, setError] = useState<string | null>(null);
 
   // Use a ref so the fetch function identity is stable.
-  const fetchRef = useRef<() => void>(() => undefined);
+  const fetchRef = useRef<() => Promise<void>>(async () => Promise.resolve());
 
   const doFetch = useCallback(async (): Promise<void> => {
     setLoading(true);
@@ -54,14 +54,14 @@ export function useServerStatus(): UseServerStatusResult {
   fetchRef.current = doFetch;
 
   // Initial fetch + polling interval.
-  useEffect(() => {
-    void doFetch();
+  useEffect((): (() => void) => {
+    void doFetch().catch((): void => undefined);
 
-    const id = setInterval(() => {
-      void fetchRef.current();
+    const id = setInterval((): void => {
+      void fetchRef.current().catch((): void => undefined);
     }, POLL_INTERVAL_MS);
 
-    return () => clearInterval(id);
+    return (): void => { clearInterval(id); };
   }, [doFetch]);
 
   // Refetch on window focus.
@@ -70,11 +70,11 @@ export function useServerStatus(): UseServerStatusResult {
       void fetchRef.current();
     };
     window.addEventListener("focus", onFocus);
-    return () => window.removeEventListener("focus", onFocus);
+    return (): void => { window.removeEventListener("focus", onFocus); };
   }, []);
 
   const refresh = useCallback((): void => {
-    void doFetch();
+    void doFetch().catch((): void => undefined);
   }, [doFetch]);
 
   return { status, loading, error, refresh };