feat(页脚组件): 新增页脚组件显示构建时间

修改package.json，添加cross-env依赖，用于在构建时设置环境变量REACT_APP_BUILD_TIME

package.json

@@ -13,7 +13,7 @@
   },
   "scripts": {
     "start": "react-scripts start",
-    "build": "react-scripts build",
+    "build": "cross-env REACT_APP_BUILD_TIME=\"%date% %time%\" react-scripts build",
     "test": "react-scripts test",
     "eject": "react-scripts eject"
   },
@@ -34,5 +34,8 @@
       "last 1 firefox version",
       "last 1 safari version"
     ]
+  },
+  "devDependencies": {
+    "cross-env": "^7.0.3"
   }
 }

src/App.js

@@ -1,12 +1,14 @@
 import React from 'react';
 import Upload from './components/Upload';
 import Setting from './components/Setting';
+import Footer from './components/Footer';
 
 function App() {
   return (
-    <div className="App">
+    <div className="App min-h-screen pb-16 relative">
       <Setting />
       <Upload />
+      <Footer />
     </div>
   );
 }

src/components/Footer.js

@@ -0,0 +1,11 @@
+import React from 'react';
+
+function Footer() {
+  return (
+    <div className="fixed bottom-0 left-0 right-0 p-4 text-center text-gray-500 text-sm bg-white border-t">
+      构建时间：{process.env.REACT_APP_BUILD_TIME || '开发环境'}
+    </div>
+  );
+}
+
+export default Footer;