feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/node_modules/d3-time-format/locale/de-DE.json

@@ -0,0 +1,10 @@
+{
+  "dateTime": "%A, der %e. %B %Y, %X",
+  "date": "%d.%m.%Y",
+  "time": "%H:%M:%S",
+  "periods": ["AM", "PM"],
+  "days": ["Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"],
+  "shortDays": ["So", "Mo", "Di", "Mi", "Do", "Fr", "Sa"],
+  "months": ["Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"],
+  "shortMonths": ["Jan", "Feb", "Mrz", "Apr", "Mai", "Jun", "Jul", "Aug", "Sep", "Okt", "Nov", "Dez"]
+}