feat(engine): 添加运行时上下文支持并重构工具迭代限制

添加 RuntimeContext 类用于捕获模型运行时的日期时间信息，
包括UTC时间、本地时间和时区信息，并在系统提示中显示这些信息。

同时增加最大上下文消息数和工具迭代次数的配置选项，
将验证服务从引擎加载器中移除，并更新相关的数据结构和接口。

BREAKING CHANGE: 移除了验证服务，相关字段被替换为证据状态和接受状态。

- 添加 RuntimeContext 类和相关渲染方法
- 增加 max_context_messages 和 max_tool_iterations 配置
- 移除 ValidationService 相关代码
- 更新消息记录中的验证状态字段
- 添加原始工具调用检测和回退处理

app-instance/backend/beaver/interfaces/web/schemas/__init__.py

@@ -1,6 +1,8 @@
 """Web request and response schemas."""
 
 from .chat import (
+    WebChatAcceptanceRequest,
+    WebChatAcceptanceResponse,
     WebChatFeedbackRequest,
     WebChatFeedbackResponse,
     WebChatRequest,
@@ -13,6 +15,8 @@ from .chat import (
 )
 
 __all__ = [
+    "WebChatAcceptanceRequest",
+    "WebChatAcceptanceResponse",
     "WebChatFeedbackRequest",
     "WebChatFeedbackResponse",
     "WebChatRequest",

app-instance/backend/beaver/interfaces/web/schemas/chat.py

@@ -82,11 +82,34 @@ class WebChatResponse(BaseModel):
     usage: dict[str, Any] = Field(default_factory=dict)
     task_id: str | None = None
     task_status: str | None = None
+    evidence_status: str | None = None
+    acceptance_state: str | None = None
     validation_result: dict[str, Any] | None = None
 
 
+class WebChatAcceptanceRequest(BaseModel):
+    """User acceptance on the latest assistant result in chat."""
+
+    session_id: str
+    run_id: str
+    acceptance_type: str
+    comment: str | None = None
+
+
+class WebChatAcceptanceResponse(BaseModel):
+    """Acceptance recording result."""
+
+    session_id: str
+    run_id: str
+    task_id: str
+    task_status: str
+    acceptance_type: str
+    feedback_type: str
+    learning_candidates: list[dict[str, Any]] = Field(default_factory=list)
+
+
 class WebChatFeedbackRequest(BaseModel):
-    """Feedback on the latest assistant result in chat."""
+    """Backward-compatible feedback payload."""
 
     session_id: str
     run_id: str
@@ -94,15 +117,8 @@ class WebChatFeedbackRequest(BaseModel):
     comment: str | None = None
 
 
-class WebChatFeedbackResponse(BaseModel):
-    """Feedback recording result."""
-
-    session_id: str
-    run_id: str
-    task_id: str
-    task_status: str
-    feedback_type: str
-    learning_candidates: list[dict[str, Any]] = Field(default_factory=list)
+class WebChatFeedbackResponse(WebChatAcceptanceResponse):
+    """Backward-compatible feedback response."""
 
 
 class WebProviderConfigRequest(BaseModel):