Fix IPv4 display and IP detection logic

Improved IP detection and display logic to always show IPv4 format, converting IPv6-mapped IPv4 addresses (e.g., ::ffff:127.0.0.1) and IPv6 loopback (::1) to 127.0.0.1. Updated API endpoint, display components, and added dedicated test/debug pages for IP format and detection. Added documentation summarizing the fixes and new features.

app/test/ip-test/page.tsx

@@ -186,6 +186,10 @@ ALLOWED_IPS=你的真實IP地址,其他允許的IP`}
           <Globe className="w-4 h-4 mr-2" />
           詳細IP調試
         </Button>
+        <Button variant="outline" onClick={() => window.open('/test/ip-format-test', '_blank')}>
+          <CheckCircle className="w-4 h-4 mr-2" />
+          IPv4格式測試
+        </Button>
         <Button variant="outline" onClick={() => window.open('/api/ip', '_blank')}>
           <ExternalLink className="w-4 h-4 mr-2" />
           IP API 端點