refactor(kernel): 移除 multi-agent feature gate — 33处 cfg 全部删除 (Phase 4A)

8 个文件移除 #[cfg(feature = "multi-agent")]，zclaw-kernel default features
新增 multi-agent。A2A 路由、agents、adapters 现在始终编译。

desktop/src-tauri/src/kernel_commands/a2a.rs

@@ -1,4 +1,4 @@
-//! A2A (Agent-to-Agent) commands — gated behind `multi-agent` feature
+//! A2A (Agent-to-Agent) commands
 
 use serde_json;
 use tauri::State;
@@ -7,10 +7,9 @@ use zclaw_types::AgentId;
 use super::KernelState;
 
 // ============================================================
-// A2A (Agent-to-Agent) Commands — gated behind multi-agent feature
+// A2A (Agent-to-Agent) Commands
 // ============================================================
 
-#[cfg(feature = "multi-agent")]
 /// Send a direct A2A message from one agent to another
 // @connected
 #[tauri::command]
@@ -44,7 +43,6 @@ pub async fn agent_a2a_send(
 }
 
 /// Broadcast a message from one agent to all other agents
-#[cfg(feature = "multi-agent")]
 // @connected
 #[tauri::command]
 pub async fn agent_a2a_broadcast(
@@ -66,7 +64,6 @@ pub async fn agent_a2a_broadcast(
 }
 
 /// Discover agents with a specific capability
-#[cfg(feature = "multi-agent")]
 // @connected
 #[tauri::command]
 pub async fn agent_a2a_discover(
@@ -88,7 +85,6 @@ pub async fn agent_a2a_discover(
   }
 
 /// Delegate a task to another agent and wait for response
-#[cfg(feature = "multi-agent")]
 // @connected
 #[tauri::command]
 pub async fn agent_a2a_delegate_task(
@@ -116,11 +112,10 @@ pub async fn agent_a2a_delegate_task(
   }
 
 // ============================================================
-// Butler Delegation Command — multi-agent feature
+// Butler Delegation Command
 // ============================================================
 
 /// Butler delegates a user request to expert agents via the Director.
-#[cfg(feature = "multi-agent")]
 // @reserved: butler multi-agent delegation
 // @connected
 #[tauri::command]