refactor: rename provider to alicode (Aliyun Coding)

Rename alicloud to alicode to clearly indicate Aliyun's Coding Plan service.

- Provider ID: alicode (short for Aliyun Coding)
- Model format: alicode/qwen3.5-plus
- Simplified mapping - no more bidirectional aliases

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/api/providers/[id]/test/route.js

@@ -464,7 +464,7 @@ async function testApiKeyConnection(connection) {
         return { valid, error: valid ? null : "Invalid API key" };
       }
 
-      case "alicloud": {
+      case "alicode": {
         // 阿里云百炼 Coding Plan uses OpenAI-compatible API
         const res = await fetch("https://coding.dashscope.aliyuncs.com/v1/chat/completions", {
           method: "POST",