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/cs-CZ.json

@@ -0,0 +1,10 @@
+{
+  "dateTime": "%A,%e.%B %Y, %X",
+  "date": "%-d.%-m.%Y",
+  "time": "%H:%M:%S",
+  "periods": ["AM", "PM"],
+  "days": ["neděle", "pondělí", "úterý", "středa", "čvrtek", "pátek", "sobota"],
+  "shortDays": ["ne.", "po.", "út.", "st.", "čt.", "pá.", "so."],
+  "months": ["leden", "únor", "březen", "duben", "květen", "červen", "červenec", "srpen", "září", "říjen", "listopad", "prosinec"],
+  "shortMonths": ["led", "úno", "břez", "dub", "kvě", "čer", "červ", "srp", "zář", "říj", "list", "pros"]
+}