fix(kernel): message_count 始终为 0 的 bug

- AgentRegistry 新增 message_counts: DashMap<AgentId, u64> 跟踪字段
- 添加 increment_message_count() 方法
- Kernel.send_message() 和 send_message_stream() 中递增计数
- get_info() 返回实际计数值而非硬编码 0

crates/zclaw-kernel/src/registry.rs

@@ -9,6 +9,7 @@ pub struct AgentRegistry {
     agents: DashMap<AgentId, AgentConfig>,
     states: DashMap<AgentId, AgentState>,
     created_at: DashMap<AgentId, chrono::DateTime<Utc>>,
+    message_counts: DashMap<AgentId, u64>,
 }
 
 impl AgentRegistry {
@@ -17,6 +18,7 @@ impl AgentRegistry {
             agents: DashMap::new(),
             states: DashMap::new(),
             created_at: DashMap::new(),
+            message_counts: DashMap::new(),
         }
     }
 
@@ -33,6 +35,7 @@ impl AgentRegistry {
         self.agents.remove(id);
         self.states.remove(id);
         self.created_at.remove(id);
+        self.message_counts.remove(id);
     }
 
     /// Get an agent by ID
@@ -53,7 +56,7 @@ impl AgentRegistry {
             model: config.model.model.clone(),
             provider: config.model.provider.clone(),
             state,
-            message_count: 0, // TODO: Track this
+            message_count: self.message_counts.get(id).map(|c| *c as usize).unwrap_or(0),
             created_at,
             updated_at: Utc::now(),
         })
@@ -83,6 +86,11 @@ impl AgentRegistry {
     pub fn count(&self) -> usize {
         self.agents.len()
     }
+
+    /// Increment message count for an agent
+    pub fn increment_message_count(&self, id: &AgentId) {
+        self.message_counts.entry(*id).and_modify(|c| *c += 1).or_insert(1);
+    }
 }
 
 impl Default for AgentRegistry {