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/single-instance.ts

@@ -1,21 +1,21 @@
-import { app } from "electron/main";
+import { app } from 'electron/main'
 
-let initialized = false;
+let initialized = false
 
 export function initSingleInstance(onSecondInstance?: () => void): boolean {
   if (initialized) {
-    return true;
+    return true
   }
 
-  initialized = true;
-  const hasLock = app.requestSingleInstanceLock();
+  initialized = true
+  const hasLock = app.requestSingleInstanceLock()
   if (!hasLock) {
-    return false;
+    return false
   }
 
-  app.on("second-instance", () => {
-    onSecondInstance?.();
-  });
+  app.on('second-instance', () => {
+    onSecondInstance?.()
+  })
 
-  return true;
+  return true
 }