feat: React 19 SPA frontend (v3.0) — volledige moderne UI op /app

- 24 pagina's: dashboard, clients, engagements, tasks, calendar, email,
  projects, time, invoices, finance, racks (visuele rack-view), networking,
  diagrams, market intel, AI studio (providers+chat), notifications,
  search, settings (algemeen/users/backup/audit)
- Vite + React 19 + Tailwind v4 + recharts + lucide, dark neon thema, NL
- Build gedeployed naar public/spa, geserveerd door Express op /app

frontend/vite.config.js

@@ -0,0 +1,22 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+import tailwindcss from '@tailwindcss/vite'
+
+export default defineConfig({
+  plugins: [react(), tailwindcss()],
+  base: '/app/',
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': {
+        target: 'http://192.168.1.247:3000',
+        changeOrigin: true
+      }
+    }
+  },
+  build: {
+    outDir: 'dist',
+    sourcemap: false,
+    chunkSizeWarningLimit: 900
+  }
+})