fix(desktop): resolve all remaining P1 defects (P1-02/05/06, P1-01 experimental)

- P1-02: Heartbeat auto-initialized in kernel_init for default agent
- P1-05: CloneManager shows warning when deleting active agent + auto-switch
- P1-06: AgentInfo returns soul/system_prompt/temperature/max_tokens
- P1-01: Browser Hand marked experimental (requires Fantoccini bridge)
- Updated DEFECT_LIST.md: all P1 resolved (0 active)
- Updated RELEASE_READINESS.md: all P1 sections reflect current status

desktop/src/components/CloneManager.tsx

@@ -31,8 +31,24 @@ export function CloneManager() {
   }, [connected, loadClones]);
 
   const handleDelete = async (id: string) => {
-    if (confirm('确定删除该分身？')) {
+    const active = useConversationStore.getState().currentAgent;
+    const isActive = active?.id === id;
+    const remainingCount = clones.length > 0 ? clones.length - 1 : agents.length - 1;
+
+    if (isActive && remainingCount <= 0) {
+      // Cannot delete the only agent
+      return;
+    }
+
+    const message = isActive
+      ? '该分身当前正在使用中，删除后将自动切换到其他分身。确定删除？'
+      : '确定删除该分身？';
+
+    if (confirm(message)) {
       await deleteClone(id);
+      // Auto-switch: syncAgents handles fallback to first remaining agent
+      const updatedClones = useAgentStore.getState().clones;
+      useChatStore.getState().syncAgents(updatedClones);
     }
   };