Add mass unban: DELETE /api/bans/all clears all active bans

- Send fail2ban's `unban --all` command via new `unban_all_ips()` service
  function; returns the count of unbanned IPs
- Add `UnbanAllResponse` Pydantic model (message + count)
- Add `DELETE /api/bans/all` router endpoint; handles 502 on socket error
- Frontend: `bansAll` endpoint constant, `unbanAllBans()` API call,
  `UnbanAllResponse` type, `unbanAll` action in `useActiveBans` hook
- JailsPage: "Clear All Bans" button (visible when bans > 0) with a
  Fluent UI confirmation Dialog before executing the operation
- 7 new tests (3 service, 4 router); 440 total pass, 82% coverage

frontend/src/hooks/useJails.ts

@@ -20,6 +20,7 @@ import {
   setJailIdle,
   startJail,
   stopJail,
+  unbanAllBans,
   unbanIp,
 } from "../api/jails";
 import type {
@@ -27,6 +28,7 @@ import type {
   IpLookupResponse,
   Jail,
   JailSummary,
+  UnbanAllResponse,
 } from "../types/jail";
 
 // ---------------------------------------------------------------------------
@@ -238,6 +240,8 @@ export interface UseActiveBansResult {
   banIp: (jail: string, ip: string) => Promise<void>;
   /** Unban an IP from a jail (or all jails when `jail` is omitted). */
   unbanIp: (ip: string, jail?: string) => Promise<void>;
+  /** Unban every currently banned IP across all jails. */
+  unbanAll: () => Promise<UnbanAllResponse>;
 }
 
 /**
@@ -293,6 +297,12 @@ export function useActiveBans(): UseActiveBansResult {
     load();
   };
 
+  const doUnbanAll = async (): Promise<UnbanAllResponse> => {
+    const result = await unbanAllBans();
+    load();
+    return result;
+  };
+
   return {
     bans,
     total,
@@ -301,6 +311,7 @@ export function useActiveBans(): UseActiveBansResult {
     refresh: load,
     banIp: doBan,
     unbanIp: doUnban,
+    unbanAll: doUnbanAll,
   };
 }