Add unit tests for API client, stores, and utils

vite.config.ts

@@ -1,3 +1,4 @@
+/// <reference types="vitest" />
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
@@ -20,4 +21,9 @@ export default defineConfig({
       },
     },
   },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: ['./src/test/setup.ts'],
+  },
 })