Add budget module and push notifications for transactions

Budget: recurring items CRUD, yearly/monthly projections with no-double-count
logic, and full UI (overview, monthly detail, recurring items manager).

Push notifications: Web Push via VAPID keys, triggered on transaction creation
from n8n. Includes service worker handlers, frontend subscription flow, and
a test button on the Dashboard (temporary).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/deploy.yml

@@ -21,6 +21,8 @@ jobs:
           ADMIN_USERNAME=${{ secrets.ADMIN_USERNAME }}
           ADMIN_PASSWORD=${{ secrets.ADMIN_PASSWORD }}
           LETSENCRYPT_EMAIL=${{ secrets.LETSENCRYPT_EMAIL }}
+          VAPID_PRIVATE_KEY=${{ secrets.VAPID_PRIVATE_KEY }}
+          VAPID_PUBLIC_KEY=${{ secrets.VAPID_PUBLIC_KEY }}
           ENVEOF
           sed -i 's/^[[:space:]]*//' .env.prod