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/react-transition-group/cjs/TransitionGroupContext.js

@@ -0,0 +1,13 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = void 0;
+
+var _react = _interopRequireDefault(require("react"));
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+var _default = _react.default.createContext(null);
+
+exports.default = _default;
+module.exports = exports.default;