feat: integrate CREEM web payment for credits purchase

Replace abandoned iOS App Store route with CREEM Merchant of Record
payment integration for web-based credits purchase.

Backend changes:
- Add CreemClient for CREEM API communication
- Add CreemService for checkout creation and webhook handling
- Add creem_transactions table for payment tracking
- Fix webhook payload parsing (id, order.id, customer.id structure)
- Integrate with existing points ledger system

Frontend changes:
- Display dynamic prices from CREEM API
- Support decimal price formatting (e.g., $1.00)
- Add checkout flow with redirect to CREEM hosted page

web/astro.config.mjs

@@ -20,11 +20,14 @@ export default defineConfig({
   vite: {
     plugins: [tailwindcss()],
     server: {
+      port: 4322,
       proxy: {
         '/api': {
-          target: 'https://api.meeyao.com',
+          target: 'http://localhost:5775',
           changeOrigin: true,
-          secure: true,
+          secure: false,
+          timeout: 30000,
+          proxyTimeout: 60000,
         },
       },
     },