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/useJails.ts

@@ -100,7 +100,7 @@ export function useJails(): UseJailsResult {
 
   useEffect(() => {
     load();
-    return () => {
+    return (): void => {
       abortRef.current?.abort();
     };
   }, [load]);
@@ -120,9 +120,9 @@ export function useJails(): UseJailsResult {
     refresh: load,
     startJail: withRefresh(startJail),
     stopJail: withRefresh(stopJail),
-    setIdle: (name, on) => setJailIdle(name, on).then(() => load()),
+    setIdle: (name, on) => setJailIdle(name, on).then((): void => { load(); }),
     reloadJail: withRefresh(reloadJail),
-    reloadAll: () => reloadAllJails().then(() => load()),
+    reloadAll: () => reloadAllJails().then((): void => { load(); }),
   };
 }
 
@@ -191,7 +191,7 @@ export function useJailDetail(name: string): UseJailDetailResult {
 
   useEffect(() => {
     load();
-    return () => {
+    return (): void => {
       abortRef.current?.abort();
     };
   }, [load]);
@@ -278,7 +278,7 @@ export function useActiveBans(): UseActiveBansResult {
 
   useEffect(() => {
     load();
-    return () => {
+    return (): void => {
       abortRef.current?.abort();
     };
   }, [load]);