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/mdn-data/css/syntaxes.schema.json

@@ -0,0 +1,15 @@
+{
+  "type": "object",
+  "additionalProperties": {
+    "type": "object",
+    "additionalProperties": false,
+    "required": [
+      "syntax"
+    ],
+    "properties": {
+      "syntax": {
+        "type": "string"
+      }
+    }
+  }
+}