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/postcss-value-parser/lib/walk.js

@@ -0,0 +1,22 @@
+module.exports = function walk(nodes, cb, bubble) {
+  var i, max, node, result;
+
+  for (i = 0, max = nodes.length; i < max; i += 1) {
+    node = nodes[i];
+    if (!bubble) {
+      result = cb(node, i, nodes);
+    }
+
+    if (
+      result !== false &&
+      node.type === "function" &&
+      Array.isArray(node.nodes)
+    ) {
+      walk(node.nodes, cb, bubble);
+    }
+
+    if (bubble) {
+      cb(node, i, nodes);
+    }
+  }
+};