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/node/IdSelector.js

@@ -0,0 +1,26 @@
+import { Hash, Delim } from '../../tokenizer/index.js';
+
+export const name = 'IdSelector';
+export const structure = {
+    name: String
+};
+
+export function parse() {
+    const start = this.tokenStart;
+
+    // TODO: check value is an ident
+    this.eat(Hash);
+
+    return {
+        type: 'IdSelector',
+        loc: this.getLocation(start, this.tokenStart),
+        name: this.substrToCursor(start + 1)
+    };
+}
+
+export function generate(node) {
+    // Using Delim instead of Hash is a hack to avoid for a whitespace between ident and id-selector
+    // in safe mode (e.g. "a#id"), because IE11 doesn't allow a sequence <ident-token> <hash-token>
+    // without a whitespace in values (e.g. "1px solid#000")
+    this.token(Delim, '#' + node.name);
+}