feat: Add CalendarSelector component and install new dependencies.

client/vite.config.js

@@ -0,0 +1,16 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    proxy: {
+      '/api': {
+        // Use 'server' for Docker Compose networking, 'localhost' for local dev
+        target: process.env.VITE_API_URL || 'http://localhost:3000',
+        changeOrigin: true,
+      },
+    },
+  },
+})