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/dom-helpers/cjs/text.d.ts

@@ -0,0 +1,8 @@
+/**
+ * Collects the text content of a given element.
+ *
+ * @param node the element
+ * @param trim whether to remove trailing whitespace chars
+ * @param singleSpaces whether to convert multiple whitespace chars into a single space character
+ */
+export default function text(node: HTMLElement | null, trim?: boolean, singleSpaces?: boolean): string;