Add unit testing infrastructure with Vitest

Set up Vitest for both server (Node + Supertest) and client (jsdom + React
Testing Library). Extract Express app into app.js for testability. Add example
tests covering bills validation, bills route CRUD, ThemeContext, and App nav
rendering. Update CLAUDE.md with testing docs and requirement to write tests
with features.

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

server/src/index.js

@@ -1,42 +1,9 @@
 require('dotenv').config();
-const express = require('express');
-const cors = require('cors');
-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 actualsRouter = require('./routes/actuals');
-const oneTimeExpensesRouter = require('./routes/one-time-expenses');
-const summaryRouter = require('./routes/summary');
-const { router: financingRouter } = require('./routes/financing');
+const app = require('./app');
 const db = require('./db');
 
-const app = express();
 const PORT = process.env.PORT || 3000;
 
-app.use(cors());
-app.use(express.json());
-
-// API routes
-app.use('/api', healthRouter);
-app.use('/api', configRouter);
-app.use('/api', billsRouter);
-app.use('/api', paychecksRouter);
-app.use('/api', actualsRouter);
-app.use('/api', oneTimeExpensesRouter);
-app.use('/api', summaryRouter);
-app.use('/api', financingRouter);
-
-// Serve static client files in production
-const clientDist = path.join(__dirname, '../../client/dist');
-app.use(express.static(clientDist));
-
-// SPA fallback — send index.html for any unmatched route
-app.get('*', (req, res) => {
-  res.sendFile(path.join(clientDist, 'index.html'));
-});
-
 (async () => {
   await db.initialize();
   app.listen(PORT, () => {