feat: Rebuild admin-ui with Preact + Signals

Complete rebuild of the admin-ui using Preact + Signals for a lightweight,
reactive framework. Features include:

- Team-centric workdesks (UI, UX, QA, Admin)
- Comprehensive API client with 150+ DSS backend endpoints
- Dark mode with system preference detection
- Keyboard shortcuts and command palette
- AI chat sidebar with Claude integration
- Toast notifications system
- Export/import functionality for project backup
- TypeScript throughout with full type coverage

Bundle size: ~66KB main (21KB gzipped), ~5KB framework overhead

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

admin-ui/tsconfig.node.json

@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "composite": true,
+    "skipLibCheck": true,
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "allowSyntheticDefaultImports": true,
+    "strict": true
+  },
+  "include": ["vite.config.ts"]
+}