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/tiny-invariant/dist/tiny-invariant.cjs.js

@@ -0,0 +1,17 @@
+'use strict';
+
+var isProduction = process.env.NODE_ENV === 'production';
+var prefix = 'Invariant failed';
+function invariant(condition, message) {
+    if (condition) {
+        return;
+    }
+    if (isProduction) {
+        throw new Error(prefix);
+    }
+    var provided = typeof message === 'function' ? message() : message;
+    var value = provided ? "".concat(prefix, ": ").concat(provided) : prefix;
+    throw new Error(value);
+}
+
+module.exports = invariant;