Add monthly summary view

GET /api/summary/monthly returns income, bills, actuals,
and one-time expense totals. Summary page shows stat cards
and a breakdown table with surplus/deficit.

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

server/src/index.js

@@ -8,6 +8,7 @@ const billsRouter = require('./routes/bills');
 const paychecksRouter = require('./routes/paychecks');
 const actualsRouter = require('./routes/actuals');
 const oneTimeExpensesRouter = require('./routes/one-time-expenses');
+const summaryRouter = require('./routes/summary');
 const db = require('./db');
 
 const app = express();
@@ -23,6 +24,7 @@ app.use('/api', billsRouter);
 app.use('/api', paychecksRouter);
 app.use('/api', actualsRouter);
 app.use('/api', oneTimeExpensesRouter);
+app.use('/api', summaryRouter);
 
 // Serve static client files in production
 const clientDist = path.join(__dirname, '../../client/dist');