feat: convert server to TypeScript + add ERP API proxy

- Migrate server/index.js → modular TS structure (config, routes, services)
- Add ERP proxy: GET /api/erp/sales proxies Hono ERP API with server-side auth
- JWT token cached server-side, auto-refreshes on 401
- ERP credentials stay server-side only (no VITE_ prefix)
- Vite dev proxy routes /api/erp → localhost:3001
- Preserve existing Salla OAuth integration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vite.config.ts

@@ -6,6 +6,10 @@ export default defineConfig({
   server: {
     port: 3000,
     proxy: {
+      '/api/erp': {
+        target: 'http://localhost:3001',
+        changeOrigin: true,
+      },
       '/api': {
         target: 'http://localhost:8090',
         changeOrigin: true,