feat(beaver): 完成Task Team功能v1实现，重构后端架构支持统一内核

新增内部Task系统，包括验证、反馈门控机制，实现自动质量验证
(通过率>=0.75)和用户反馈闭环(satisfied/revise/abandon)。

实现Agent Team v1协调器，支持sequence/parallel/dag执行策略，
sub-agent复用主AgentLoop，每个run使用独立memory snapshot。

建立Skill学习pipeline，包含draft/审核/发布/回滚完整生命周期，
通过Task验证通过且用户满意才生成学习候选。

重构目录结构，移除third_party依赖，建立统一engine内核，
所有agent共享运行时基础组件。

更新ContextBuilder清理provider消息字段，增强SkillContext版本管理，
集成TaskExecutionPlanner和TaskSkillResolver实现技能解析机制。

app-instance/backend/beaver/engine/context/builder.py

@@ -42,6 +42,10 @@ class SkillContext:
 
     name: str
     content: str
+    version: str = "legacy"
+    content_hash: str = ""
+    activation_reason: str = "selected"
+    tool_hints: list[str] = field(default_factory=list)
 
 
 @dataclass(slots=True)
@@ -197,7 +201,7 @@ class ContextBuilder:
             # 如果上游 history 已经混入 system 消息，这里要主动跳过，避免双 system。
             if message.get("role") == "system":
                 continue
-            messages.append(dict(message))
+            messages.append(self._provider_history_message(message))
 
         if build_input.current_user_input is not None:
             messages.append(
@@ -212,6 +216,16 @@ class ContextBuilder:
             messages=messages,
         )
 
+    @staticmethod
+    def _provider_history_message(message: dict[str, Any]) -> dict[str, Any]:
+        """Keep persisted UI/audit fields out of provider message payloads."""
+
+        allowed = {"role", "content", "tool_calls", "tool_call_id", "name"}
+        clean = {key: value for key, value in message.items() if key in allowed}
+        if "name" not in clean and message.get("tool_name"):
+            clean["name"] = message.get("tool_name")
+        return clean
+
     def add_tool_result(
         self,
         messages: list[dict[str, Any]],
@@ -322,7 +336,7 @@ class ContextBuilder:
                 {
                     "role": "user",
                     "content": (
-                        f'[SYSTEM: The "{skill.name}" skill is active for this run. '
+                        f'[SYSTEM: The "{skill.name}" skill (version {skill.version}) is active for this run. '
                         "Follow its instructions as active guidance unless the user overrides them.]\n\n"
                         f"{content}"
                     ),