chore(frontend): introduce prettier + eslint and prune unused code

- Add Prettier 3 with prettier-plugin-organize-imports (sorts/removes unused imports)
- Add ESLint 10 flat config with typescript-eslint + eslint-plugin-vue + eslint-config-prettier
- Add root scripts: format, format:check, lint, lint:fix
- Reformat 257 files across admin-web, ops-web, desktop-client, packages
- Remove unused locals/exports flagged by --noUnusedLocals/--noUnusedParameters
- Fix duplicate localTabLabel key, surrogate-pair regex u-flag, NBSP literal in regex
- Skip server/ (Go) and apps/browser-extension/ (deprecated per ADR)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/main/keep-alive.ts

@@ -1,18 +1,18 @@
 interface KeepAlivePlan {
-  mode: "probe-only" | "heartbeat" | "disabled";
-  updatedAt: number;
+  mode: 'probe-only' | 'heartbeat' | 'disabled'
+  updatedAt: number
 }
 
 const keepAlivePlan: KeepAlivePlan = {
-  mode: "probe-only",
+  mode: 'probe-only',
   updatedAt: Date.now(),
-};
+}
 
-export function updateKeepAlivePlan(mode: KeepAlivePlan["mode"]): void {
-  keepAlivePlan.mode = mode;
-  keepAlivePlan.updatedAt = Date.now();
+export function updateKeepAlivePlan(mode: KeepAlivePlan['mode']): void {
+  keepAlivePlan.mode = mode
+  keepAlivePlan.updatedAt = Date.now()
 }
 
 export function getKeepAlivePlan(): KeepAlivePlan {
-  return { ...keepAlivePlan };
+  return { ...keepAlivePlan }
 }