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>

.prettierignore

@@ -0,0 +1,38 @@
+# Dependencies
+node_modules
+
+# Build output
+dist
+build
+out
+release
+.output
+.wxt
+
+# Generated artifacts
+**/dist/**
+**/build/**
+**/out/**
+**/release/**
+**/.output/**
+**/stats.html
+**/components.d.ts
+**/auto-imports.d.ts
+
+# Lockfiles & generated data
+pnpm-lock.yaml
+package-lock.json
+yarn.lock
+
+# Server (Go) — Prettier shouldn't touch Go
+server
+
+# Browser extension is being phased out — skip to avoid noisy diff
+apps/browser-extension
+
+# Misc
+*.min.js
+*.min.css
+coverage
+.cache
+.vite