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/css.escape/README.md

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+# `CSS.escape` polyfill [![Build status](https://travis-ci.org/mathiasbynens/CSS.escape.svg?branch=master)](https://travis-ci.org/mathiasbynens/CSS.escape) [![Code coverage status](http://img.shields.io/coveralls/mathiasbynens/CSS.escape/master.svg)](https://coveralls.io/r/mathiasbynens/CSS.escape)
+
+A robust polyfill for [the `CSS.escape` utility method as defined in CSSOM](https://drafts.csswg.org/cssom/#the-css.escape%28%29-method).
+
+For a more powerful alternative, consider using [cssesc](https://mths.be/cssesc), which automatically takes care of excessive whitespace, and has many options to customize the output.
+
+## Installation
+
+In a browser:
+
+```html
+<script src="css.escape.js"></script>
+```
+
+Via [npm](https://www.npmjs.com/):
+
+```bash
+npm install css.escape
+```
+
+Then, in [Node.js](https://nodejs.org/):
+
+```js
+require('css.escape');
+
+// On Windows and on Mac systems with default settings, case doesn’t matter,
+// which allows you to do this instead:
+require('CSS.escape');
+```
+
+## Author
+
+| [![twitter/mathias](https://gravatar.com/avatar/24e08a9ea84deb17ae121074d0f17125?s=70)](https://twitter.com/mathias "Follow @mathias on Twitter") |
+|---|
+| [Mathias Bynens](https://mathiasbynens.be/) |
+
+## License
+
+This polyfill is available under the [MIT](https://mths.be/mit) license.