fix: 媒体技能改用动态 provider 发现，移除硬编码 providerId

minimax-music-gen (1.1.2 → 1.1.3):
- providerId: "provider-minimax-media-001" → provider: "minimax" + serviceType: "music_gen"

minimax-video-gen (1.2.1 → 1.2.2):
- providerId: "provider-minimax-media-001" → provider: "minimax" + serviceType: "video_gen"

此前硬编码的 provider-minimax-media-001 在系统中不存在，导致使用
MiniMax Token Plan 或 Coding Plan 时文生音乐/文生视频功能无法路由。
改为 slug + serviceType 动态发现后，无论用户启用按量 API 还是
Token/Coding Plan，findProvider() 都能正确匹配。

skills/minimax-music-gen/SKILL.zh-CN.md

@@ -58,7 +58,8 @@ PORT=$(cat ~/.desirecore/agent-service.port)
 curl -sk -X POST "https://127.0.0.1:${PORT}/api/media-proxy" \
   -H "Content-Type: application/json" \
   -d '{
-    "providerId": "provider-minimax-media-001",
+    "provider": "minimax",
+    "serviceType": "music_gen",
     "endpoint": "/music_generation",
     "body": {
       "model": "music-2.6",
@@ -81,7 +82,8 @@ PORT=$(cat ~/.desirecore/agent-service.port)
 curl -sk -X POST "https://127.0.0.1:${PORT}/api/media-proxy" \
   -H "Content-Type: application/json" \
   -d '{
-    "providerId": "provider-minimax-media-001",
+    "provider": "minimax",
+    "serviceType": "music_gen",
     "endpoint": "/music_generation",
     "body": {
       "model": "music-2.6",
@@ -194,7 +196,8 @@ PORT=$(cat ~/.desirecore/agent-service.port)
 curl -sk -X POST "https://127.0.0.1:${PORT}/api/media-proxy" \
   -H "Content-Type: application/json" \
   -d '{
-    "providerId": "provider-minimax-media-001",
+    "provider": "minimax",
+    "serviceType": "music_gen",
     "endpoint": "/music_generation",
     "body": {
       "model": "music-2.6",
@@ -217,7 +220,7 @@ curl -sk -X POST "https://127.0.0.1:${PORT}/api/media-proxy" \
 - `base_resp.status_code: 1008`：余额不足
 - `base_resp.status_code: 1026`：内容敏感，修改歌词或 prompt 后重试
 - `base_resp.status_code: 2013`：参数错误，检查必填字段
-- `success: false` + `error: "未找到匹配的供应商"`：未配置 MiniMax Provider
+- `success: false` + `error: "未找到匹配的供应商"`：未找到已启用且支持 `music_gen` 服务的 MiniMax Provider
 
 ### 注意事项