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/vite.config.ts

@@ -0,0 +1,77 @@
+import { defineConfig } from 'vite';
+import preact from '@preact/preset-vite';
+import { VitePWA } from 'vite-plugin-pwa';
+import { resolve } from 'path';
+
+export default defineConfig({
+  plugins: [
+    preact(),
+    VitePWA({
+      registerType: 'autoUpdate',
+      includeAssets: ['favicon.ico', 'robots.txt', 'apple-touch-icon.png'],
+      manifest: {
+        name: 'DSS Admin',
+        short_name: 'DSS',
+        description: 'Design System Server Administration',
+        theme_color: '#0f172a',
+        background_color: '#ffffff',
+        display: 'standalone',
+        icons: [
+          {
+            src: 'pwa-192x192.png',
+            sizes: '192x192',
+            type: 'image/png'
+          },
+          {
+            src: 'pwa-512x512.png',
+            sizes: '512x512',
+            type: 'image/png'
+          }
+        ]
+      },
+      workbox: {
+        globPatterns: ['**/*.{js,css,html,ico,png,svg}'],
+        runtimeCaching: [
+          {
+            urlPattern: /^\/api\/.*/i,
+            handler: 'NetworkFirst',
+            options: {
+              cacheName: 'api-cache',
+              expiration: {
+                maxEntries: 100,
+                maxAgeSeconds: 60 * 60 // 1 hour
+              }
+            }
+          }
+        ]
+      }
+    })
+  ],
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, './src'),
+      'react': 'preact/compat',
+      'react-dom': 'preact/compat'
+    }
+  },
+  server: {
+    port: 3456,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:8002',
+        changeOrigin: true
+      }
+    }
+  },
+  build: {
+    outDir: 'dist',
+    sourcemap: true,
+    rollupOptions: {
+      output: {
+        manualChunks: {
+          'preact': ['preact', '@preact/signals']
+        }
+      }
+    }
+  }
+});