fix: spawn_workers skill 名称修正 — airplan → airplan-v2:do

skill 目录名是 airplan-v2，不是 airplan。Claude Code 按目录名注册。
正确的 Skill 调用格式为 Skill("airplan-v2:do")。

同步更新：
- eng_mode.py spawn_workers() 返回值
- commands/eng.md dispatch 操作步骤
- test_t_121_122.py 测试断言
- 设计文档 3.2.11b spawn_workers 伪代码

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

test_t_121_122.py

@@ -29,8 +29,8 @@ def test_spawn_workers():
 
         instructions = spawn_workers(root, ["G-001", "G-002"])
         assert len(instructions) == 2
-        assert instructions[0]["skill"] == "airplan"
-        assert "do --sub enter --task-id G-001" in instructions[0]["args"]
+        assert instructions[0]["skill"] == "airplan-v2:do"
+        assert "--sub enter --task-id G-001" in instructions[0]["args"]
         assert "实现视频解码器" in instructions[0]["args"]
         assert instructions[1]["taskId"] == "G-002"
 
@@ -151,8 +151,8 @@ def test_full_pipeline_e2e():
         instructions = spawn_workers(root, dispatch["taskIds"])
         assert len(instructions) >= 2
         for inst in instructions:
-            assert inst["skill"] == "airplan"
-            assert "do --sub enter --task-id" in inst["args"]
+            assert inst["skill"] == "airplan-v2:do"
+            assert "--sub enter --task-id" in inst["args"]
             assert inst["taskText"]  # 不能为空
         print(f"4. spawn_workers: {len(instructions)} 个 Worker 指令准备完成")
         for inst in instructions: