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/scope/value.js

@@ -0,0 +1,25 @@
+import getNode from './default.js';
+import expressionFn from '../function/expression.js';
+import varFn from '../function/var.js';
+
+function isPlusMinusOperator(node) {
+    return (
+        node !== null &&
+        node.type === 'Operator' &&
+        (node.value[node.value.length - 1] === '-' || node.value[node.value.length - 1] === '+')
+    );
+}
+
+export default {
+    getNode,
+    onWhiteSpace(next, children) {
+        if (isPlusMinusOperator(next)) {
+            next.value = ' ' + next.value;
+        }
+        if (isPlusMinusOperator(children.last)) {
+            children.last.value += ' ';
+        }
+    },
+    'expression': expressionFn,
+    'var': varFn
+};