fix: Generate Vite manifest for customer SPA loading

Problem: Customer SPA stuck on 'Loading...' message after installation
Root Cause: Vite build wasn't generating manifest.json, causing WordPress asset loader to fall back to direct app.js loading without proper module configuration

Solution:
1. Added manifest: true to both SPA vite configs
2. Updated Assets.php to look for manifest in correct location (.vite/manifest.json)
3. Rebuilt both SPAs with manifest generation

Changes:
- customer-spa/vite.config.ts: Added manifest: true
- admin-spa/vite.config.ts: Added manifest: true
- includes/Frontend/Assets.php: Updated manifest path from 'manifest.json' to '.vite/manifest.json'

Build Output:
- Customer SPA: dist/.vite/manifest.json generated
- Admin SPA: dist/.vite/manifest.json generated
- Production zip: 10M (includes manifest files)

Result:
✅ Customer SPA now loads correctly via manifest
✅ Admin SPA continues to work
✅ Proper asset loading with CSS and JS from manifest
✅ Production package ready for deployment

admin-spa/vite.config.ts

@@ -21,6 +21,7 @@ export default defineConfig({
   build: {
     outDir: 'dist',
     emptyOutDir: true,
+    manifest: true,
     rollupOptions: {
       input: { app: 'src/main.tsx' },
       output: { entryFileNames: 'app.js', assetFileNames: 'app.[ext]' }