refactor: migrate API routes to Hono sub-router

- Create Hono router in api.ts
- Convert 6 API endpoints to Hono format:
  - GET /api/deposit/balance
  - POST /api/deposit/deduct
  - POST /api/test
  - POST /api/chat
  - POST /api/contact
  - GET /api/metrics
- Use Hono CORS middleware for /contact
- Remove manual handleApiRequest and handleContactPreflight
- Integrate with main app via app.route('/api', apiRouter)

Benefits:
- Cleaner declarative routing (44 insertions, 48 deletions)
- Built-in CORS middleware
- Better code organization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/index.ts

@@ -1,7 +1,7 @@
 import { Env, EmailMessage, ProvisionMessage, MessageBatch } from './types';
 import { sendMessage, setWebhook, getWebhookInfo } from './telegram';
 import { handleWebhook } from './routes/webhook';
-import { handleApiRequest } from './routes/api';
+import { apiRouter } from './routes/api';
 import { handleHealthCheck } from './routes/health';
 import { parseBankSMS } from './services/bank-sms-parser';
 import { matchPendingDeposit } from './services/deposit-matcher';
@@ -69,8 +69,8 @@ app.get('/webhook-info', async (c) => {
   return c.json(result);
 });
 
-// API routes
-app.all('/api/*', (c) => handleApiRequest(c.req.raw, c.env, new URL(c.req.url)));
+// API routes - use Hono router
+app.route('/api', apiRouter);
 
 // Telegram Webhook
 app.post('/webhook', (c) => handleWebhook(c.req.raw, c.env));