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/@testing-library/dom/dist/queries/placeholder-text.js

@@ -0,0 +1,22 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.queryByPlaceholderText = exports.queryAllByPlaceholderText = exports.getByPlaceholderText = exports.getAllByPlaceholderText = exports.findByPlaceholderText = exports.findAllByPlaceholderText = void 0;
+var _queryHelpers = require("../query-helpers");
+var _helpers = require("../helpers");
+var _allUtils = require("./all-utils");
+const queryAllByPlaceholderText = (...args) => {
+  (0, _helpers.checkContainerType)(args[0]);
+  return (0, _allUtils.queryAllByAttribute)('placeholder', ...args);
+};
+const getMultipleError = (c, text) => `Found multiple elements with the placeholder text of: ${text}`;
+const getMissingError = (c, text) => `Unable to find an element with the placeholder text of: ${text}`;
+const queryAllByPlaceholderTextWithSuggestions = exports.queryAllByPlaceholderText = (0, _queryHelpers.wrapAllByQueryWithSuggestion)(queryAllByPlaceholderText, queryAllByPlaceholderText.name, 'queryAll');
+const [queryByPlaceholderText, getAllByPlaceholderText, getByPlaceholderText, findAllByPlaceholderText, findByPlaceholderText] = (0, _allUtils.buildQueries)(queryAllByPlaceholderText, getMultipleError, getMissingError);
+exports.findByPlaceholderText = findByPlaceholderText;
+exports.findAllByPlaceholderText = findAllByPlaceholderText;
+exports.getByPlaceholderText = getByPlaceholderText;
+exports.getAllByPlaceholderText = getAllByPlaceholderText;
+exports.queryByPlaceholderText = queryByPlaceholderText;