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/tiny-invariant/dist/tiny-invariant.js

@@ -0,0 +1,23 @@
+(function (global, factory) {
+    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
+    typeof define === 'function' && define.amd ? define(factory) :
+    (global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.invariant = factory());
+})(this, (function () { 'use strict';
+
+    var isProduction = process.env.NODE_ENV === 'production';
+    var prefix = 'Invariant failed';
+    function invariant(condition, message) {
+        if (condition) {
+            return;
+        }
+        if (isProduction) {
+            throw new Error(prefix);
+        }
+        var provided = typeof message === 'function' ? message() : message;
+        var value = provided ? "".concat(prefix, ": ").concat(provided) : prefix;
+        throw new Error(value);
+    }
+
+    return invariant;
+
+}));