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]/home/year-month/[id]/add/page.tsx

@@ -0,0 +1,13 @@
+import { addMonth } from '@/app/lib/actions/monthActions';
+import { gotoHome } from '@/app/lib/actions/navigationActions';
+import { parseYearMonth } from '@/app/lib/format';
+
+export default async function Page({ params:{ id } }: { params: { id:string } }) {
+
+    const { year, month } = parseYearMonth(id);
+    await addMonth({ year, month });
+
+    await gotoHome({ year, month });
+
+    return null; // if we don't return anything, the client-side will not re-validate cache
+}