refactor: convert repository to monorepo with npm workspaces

Restructured the repository into a monorepo to better organize application code
and maintenance scripts.

## Workspace Structure
- web-app: Next.js application (all app code moved from root)
- housekeeping: Database backup and maintenance scripts

## Key Changes
- Moved all application code to web-app/ using git mv
- Moved database scripts to housekeeping/ workspace
- Updated Dockerfile for monorepo build process
- Updated docker-compose files (volume paths: ./web-app/etc/hosts/)
- Updated .gitignore for workspace-level node_modules
- Updated documentation (README.md, CLAUDE.md, CHANGELOG.md)

## Migration Impact
- Root package.json now manages workspaces
- Build commands delegate to web-app workspace
- All file history preserved via git mv
- Docker build process updated for workspace structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

web-app/app/lib/dbClient.ts

@@ -0,0 +1,40 @@
+import { MongoClient } from 'mongodb'
+
+if (!process.env.MONGODB_URI) {
+  throw new Error('Invalid environment variable: "MONGODB_URI"')
+}
+
+const uri = process.env.MONGODB_URI
+const options = { }
+
+let client
+let clientPromise: Promise<MongoClient>
+
+
+if (!process.env.MONGODB_URI) {
+  throw new Error('Please add your Mongo URI to .env.local')
+}
+
+if (process.env.NODE_ENV === 'development') {
+  // In development mode, use a global variable so that the value
+  // is preserved across module reloads caused by HMR (Hot Module Replacement).
+  if (!global._mongoClientPromise) {
+    client = new MongoClient(uri, options)
+    global._mongoClientPromise = client.connect()
+  }
+  clientPromise = global._mongoClientPromise
+} else {
+  // In production mode, it's best to not use a global variable.
+  client = new MongoClient(uri, options)
+  clientPromise = client.connect()
+}
+
+// Export a module-scoped MongoClient promise. By doing this in a
+// separate module, the client can be shared across functions.
+export default clientPromise
+
+export const getDbClient = async () => {
+  const client = await clientPromise;
+  const db = client.db("utility-bills");
+  return(db);
+}