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/resolve/lib/homedir.js

@@ -0,0 +1,31 @@
+'use strict';
+
+var os = require('os');
+
+// adapted from https://github.com/sindresorhus/os-homedir/blob/11e089f4754db38bb535e5a8416320c4446e8cfd/index.js
+
+module.exports = os.homedir || function homedir() {
+    var home = process.env.HOME;
+    var user = process.env.LOGNAME || process.env.USER || process.env.LNAME || process.env.USERNAME;
+
+    if (process.platform === 'win32') {
+        return process.env.USERPROFILE
+            || (
+                process.env.HOMEDRIVE
+                && process.env.HOMEPATH
+                && (process.env.HOMEDRIVE + process.env.HOMEPATH)
+            )
+            || home
+            || null;
+    }
+
+    if (process.platform === 'darwin') {
+        return home || (user ? '/Users/' + user : null);
+    }
+
+    if (process.platform === 'linux') {
+        return home || (process.getuid() === 0 ? '/root' : (user ? '/home/' + user : null)); // eslint-disable-line no-extra-parens
+    }
+
+    return home || null;
+};