feat: implement Phase 2 (Go Agent) and Phase 3 (React Frontend MVP)

Phase 2 - Go Agent Core:
- gRPC client with exponential backoff reconnect logic
- Command executor (PowerShell/sh cross-platform)
- Proto stubs regenerated with module= option (correct output path)
- gRPC upgraded to v1.79.3 (BidiStreamingClient support)

Phase 3 - React Frontend MVP:
- Vite + React 18 + TypeScript setup with Tailwind CSS v4
- TanStack Query for data fetching, API client + TypeScript types
- Dashboard page: stats cards (agents/status/tickets) + sortable agents table
- Agent detail page: CPU/RAM charts (Recharts), disk usage, shell command executor
- Tickets page: CRUD with modals, filters, sortable table
- Dark mode with CSS custom properties

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Frontend/vite.config.ts

@@ -0,0 +1,29 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+import tailwindcss from '@tailwindcss/vite'
+import path from 'path'
+
+export default defineConfig({
+  plugins: [
+    react(),
+    tailwindcss(),
+  ],
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, './src'),
+    },
+  },
+  server: {
+    proxy: {
+      '/api': {
+        target: 'http://localhost:5000',
+        changeOrigin: true,
+      },
+      '/hubs': {
+        target: 'http://localhost:5000',
+        changeOrigin: true,
+        ws: true,
+      },
+    },
+  },
+})