Add paycheck generation and retrieval API

Auto-generates paycheck records from config and active bills.
GET /api/paychecks auto-generates if month not yet created.
Idempotent generation preserves existing paid status.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/index.js

@@ -5,6 +5,7 @@ const path = require('path');
 const healthRouter = require('./routes/health');
 const configRouter = require('./routes/config');
 const billsRouter = require('./routes/bills');
+const paychecksRouter = require('./routes/paychecks');
 const db = require('./db');
 
 const app = express();
@@ -17,6 +18,7 @@ app.use(express.json());
 app.use('/api', healthRouter);
 app.use('/api', configRouter);
 app.use('/api', billsRouter);
+app.use('/api', paychecksRouter);
 
 // Serve static client files in production
 const clientDist = path.join(__dirname, '../../client/dist');