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-tree/lib/syntax/atrule/import.js

@@ -0,0 +1,39 @@
+import {
+    String as StringToken,
+    Ident,
+    Url,
+    Function as FunctionToken,
+    LeftParenthesis
+} from '../../tokenizer/index.js';
+
+export default {
+    parse: {
+        prelude() {
+            const children = this.createList();
+
+            this.skipSC();
+
+            switch (this.tokenType) {
+                case StringToken:
+                    children.push(this.String());
+                    break;
+
+                case Url:
+                case FunctionToken:
+                    children.push(this.Url());
+                    break;
+
+                default:
+                    this.error('String or url() is expected');
+            }
+
+            if (this.lookupNonWSType(0) === Ident ||
+                this.lookupNonWSType(0) === LeftParenthesis) {
+                children.push(this.MediaQueryList());
+            }
+
+            return children;
+        },
+        block: null
+    }
+};