Add bills CRUD API and management UI

Full REST API for bill definitions with validation.
Bills page supports add, edit, toggle active, and delete.

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

server/src/index.js

@@ -4,6 +4,7 @@ const cors = require('cors');
 const path = require('path');
 const healthRouter = require('./routes/health');
 const configRouter = require('./routes/config');
+const billsRouter = require('./routes/bills');
 const db = require('./db');
 
 const app = express();
@@ -15,6 +16,7 @@ app.use(express.json());
 // API routes
 app.use('/api', healthRouter);
 app.use('/api', configRouter);
+app.use('/api', billsRouter);
 
 // Serve static client files in production
 const clientDist = path.join(__dirname, '../../client/dist');