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]/share/proof-of-payment/per-bill/[id]/not-found.tsx

@@ -0,0 +1,7 @@
+export default function NotFound() {
+    return (
+        <div className="flex min-h-screen flex-col items-center justify-center p-6 bg-base-300">
+            <h2 className="text-2xl font-bold">Proof of payment not found</h2>
+        </div>
+    );
+}

web-app/app/[locale]/share/proof-of-payment/per-bill/[id]/route.tsx

@@ -0,0 +1,70 @@
+import { getDbClient } from '@/app/lib/dbClient';
+import { BillingLocation } from '@/app/lib/db-types';
+import { notFound } from 'next/navigation';
+import { extractShareId, validateShareChecksum } from '@/app/lib/shareChecksum';
+
+export async function GET(_request: Request, { params: { id } }: { params: { id: string } }) {
+    // Parse shareId-billID format
+    // shareId = 40 chars (locationId 24 + checksum 16)
+    const shareId = id.substring(0, 40);
+    const billID = id.substring(41); // Skip the '-' separator
+
+    if (!shareId || !billID) {
+        notFound();
+    }
+
+    // Validate shareId and extract locationId
+    const extracted = extractShareId(shareId);
+    if (!extracted) {
+        notFound();
+    }
+
+    const { locationId: locationID, checksum } = extracted;
+
+    // Validate checksum
+    if (!validateShareChecksum(locationID, checksum)) {
+        notFound();
+    }
+
+    const dbClient = await getDbClient();
+    const location = await dbClient.collection<BillingLocation>("lokacije")
+        .findOne({ _id: locationID }, {
+            projection: {
+                // Don't load bill attachments, only proof of payment and shareTTL
+                "bills._id": 1,
+                "bills.proofOfPayment": 1,
+                "shareTTL": 1,
+            }
+        });
+
+    if (!location) {
+        notFound();
+    }
+
+    // Check if sharing is active and not expired
+    if (!location.shareTTL || new Date() > location.shareTTL) {
+        notFound();
+    }
+
+    // Find the specific bill
+    const bill = location.bills.find(b => b._id === billID);
+
+    if(!bill?.proofOfPayment) {
+        notFound();
+    }
+
+    // Convert fileContentsBase64 from Base64 string to binary
+    const fileContentsBuffer = Buffer.from(bill.proofOfPayment.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/pdf',
+            'Content-Disposition': `attachment; filename="${bill.proofOfPayment.fileName}"`,
+            'Last-Modified': `${bill.proofOfPayment.fileLastModified}`
+        }
+    });
+}