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/@babel/runtime/regenerator/index.js

@@ -0,0 +1,15 @@
+// TODO(Babel 8): Remove this file.
+
+var runtime = require("../helpers/regeneratorRuntime")();
+module.exports = runtime;
+
+// Copied from https://github.com/facebook/regenerator/blob/main/packages/runtime/runtime.js#L736=
+try {
+  regeneratorRuntime = runtime;
+} catch (accidentalStrictMode) {
+  if (typeof globalThis === "object") {
+    globalThis.regeneratorRuntime = runtime;
+  } else {
+    Function("r", "regeneratorRuntime = r")(runtime);
+  }
+}