fix(runtime,kernel): HandTool 空壳修复 — 桥接到 HandRegistry 真实执行

B-HAND-1 修复: LLM 调用 hand_quiz/hand_researcher 等 Hand 工具后,
HandTool::execute() 原来返回假成功 JSON, 实际 Hand 并不执行.

修复方案 (沿用 SkillExecutor 模式):
- tool.rs: 新增 HandExecutor trait + ToolContext.hand_executor 字段
- hand_tool.rs: execute() 通过 context.hand_executor 分发到真实执行
- loop_runner.rs: AgentLoop 新增 hand_executor 字段 + builder + 3处 ToolContext 传递
- adapters.rs: 新增 KernelHandExecutor 桥接 HandRegistry.execute()
- kernel/mod.rs: 初始化 KernelHandExecutor + 注册到 AgentLoop
- messaging.rs: 两处 AgentLoop 构建添加 .with_hand_executor()

数据流: LLM tool call → HandTool::execute() → ToolContext.hand_executor
         → KernelHandExecutor → HandRegistry.execute() → Hand trait impl

809 tests passed, 0 failed.

crates/zclaw-runtime/src/tool/builtin/file_read.rs

@@ -139,6 +139,7 @@ mod tests {
             working_directory: None,
             session_id: None,
             skill_executor: None,
+            hand_executor: None,
             path_validator,
             event_sender: None,
         };

crates/zclaw-runtime/src/tool/builtin/file_write.rs

@@ -162,6 +162,7 @@ mod tests {
             working_directory: None,
             session_id: None,
             skill_executor: None,
+            hand_executor: None,
             path_validator,
             event_sender: None,
         }