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/da-DK.json

@@ -0,0 +1,10 @@
+{
+  "dateTime": "%A den %d %B %Y %X",
+  "date": "%d-%m-%Y",
+  "time": "%H:%M:%S",
+  "periods": ["AM", "PM"],
+  "days": ["søndag", "mandag", "tirsdag", "onsdag", "torsdag", "fredag", "lørdag"],
+  "shortDays": ["søn", "man", "tir", "ons", "tor", "fre", "lør"],
+  "months": ["januar", "februar", "marts", "april", "maj", "juni", "juli", "august", "september", "oktober", "november", "december"],
+  "shortMonths": ["jan", "feb", "mar", "apr", "maj", "jun", "jul", "aug", "sep", "okt", "nov", "dec"]
+}