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/[locale]/attachment/[id]/not-found.tsx

@@ -0,0 +1,6 @@
+import { NotFoundPage } from '@/app/ui/NotFoundPage';
+ 
+const AttachmentNotFound = () =>
+<NotFoundPage title="404 File Not Found" description="Could not find the requested attachment." />;
+
+export default AttachmentNotFound;

web-app/app/[locale]/attachment/[id]/route.tsx

@@ -0,0 +1,27 @@
+import { fetchBillById } from '@/app/lib/actions/billActions';
+import { notFound } from 'next/navigation';
+
+export async function GET(request: Request, { params:{ id } }: { params: { id:string } }) {
+    const [locationID, billID] = id.split('-');
+
+    const [location, bill] = await fetchBillById(locationID, billID, true) ?? [];
+
+    if(!bill?.attachment) {
+        notFound();
+    }
+
+    // convert fileContentsBase64 from Base64 string to binary string
+    const fileContentsBuffer = Buffer.from(bill.attachment.fileContentsBase64, 'base64');
+
+    // convert fileContentsBuffer to format that can be sent to the client
+    const fileContents = new Uint8Array(fileContentsBuffer);
+    
+    return new Response(fileContents, {
+        status: 200,
+        headers: {
+            'Content-Type': "application/octet-stream",
+            'Content-Disposition': `attachment; filename="${bill.attachment.fileName}"`,
+            'Last-Modified': `${bill.attachment.fileLastModified}`
+        }
+    });
+}