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/react-dom/client.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var m = require('react-dom');
+if (process.env.NODE_ENV === 'production') {
+  exports.createRoot = m.createRoot;
+  exports.hydrateRoot = m.hydrateRoot;
+} else {
+  var i = m.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED;
+  exports.createRoot = function(c, o) {
+    i.usingClientEntryPoint = true;
+    try {
+      return m.createRoot(c, o);
+    } finally {
+      i.usingClientEntryPoint = false;
+    }
+  };
+  exports.hydrateRoot = function(c, h, o) {
+    i.usingClientEntryPoint = true;
+    try {
+      return m.hydrateRoot(c, h, o);
+    } finally {
+      i.usingClientEntryPoint = false;
+    }
+  };
+}