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/p-limit/index.js

@@ -0,0 +1,71 @@
+import Queue from 'yocto-queue';
+import {AsyncResource} from '#async_hooks';
+
+export default function pLimit(concurrency) {
+	if (!((Number.isInteger(concurrency) || concurrency === Number.POSITIVE_INFINITY) && concurrency > 0)) {
+		throw new TypeError('Expected `concurrency` to be a number from 1 and up');
+	}
+
+	const queue = new Queue();
+	let activeCount = 0;
+
+	const next = () => {
+		activeCount--;
+
+		if (queue.size > 0) {
+			queue.dequeue()();
+		}
+	};
+
+	const run = async (function_, resolve, arguments_) => {
+		activeCount++;
+
+		const result = (async () => function_(...arguments_))();
+
+		resolve(result);
+
+		try {
+			await result;
+		} catch {}
+
+		next();
+	};
+
+	const enqueue = (function_, resolve, arguments_) => {
+		queue.enqueue(
+			AsyncResource.bind(run.bind(undefined, function_, resolve, arguments_)),
+		);
+
+		(async () => {
+			// This function needs to wait until the next microtask before comparing
+			// `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
+			// when the run function is dequeued and called. The comparison in the if-statement
+			// needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
+			await Promise.resolve();
+
+			if (activeCount < concurrency && queue.size > 0) {
+				queue.dequeue()();
+			}
+		})();
+	};
+
+	const generator = (function_, ...arguments_) => new Promise(resolve => {
+		enqueue(function_, resolve, arguments_);
+	});
+
+	Object.defineProperties(generator, {
+		activeCount: {
+			get: () => activeCount,
+		},
+		pendingCount: {
+			get: () => queue.size,
+		},
+		clearQueue: {
+			value() {
+				queue.clear();
+			},
+		},
+	});
+
+	return generator;
+}