feat(cli): /persona 与 /agents 对齐 WebUI（复用已开放的 SDK 面）

- /persona：读写 core.agent.personal_prompt / core.internal.persona_initialized；
  插件 SDK 的 Settings() 满足 internal/config.PersonaKV，与 WebUI 同一实现。
  GET 等价返回 initialized/current_prompt/file_override；/persona set <mode> [内容] 写。
- /agents：改用 supervisor.ListAgents()（WebUI /agents 同源），此前只回一个
  agent_id、驻留子信息全丢。
- waiter 侧 /persona 在 local/remote 两条路都接上，/help 补齐。

cmd/waiter/builtin.go

@@ -47,6 +47,7 @@ Server commands (local 与 remote 行为一致):
   /adapters remove <name>  remove a Lua adapter
   /network                 network status + LLM endpoints
   /runtime                 scheduler / residents / channel topology
+  /persona                 show persona (/persona set default|custom|later [text])
   /agents                  list agents
   /chat <text>             send to agent
 
@@ -330,6 +331,28 @@ Any other text is sent to the agent directly.`)
 		}
 		return true
 
+	case cmd == "/persona" || strings.HasPrefix(cmd, "/persona set "):
+		if rc := state.RemoteConn(); rc != nil {
+			if strings.HasPrefix(cmd, "/persona set ") {
+				rest := strings.TrimSpace(cmd[13:])
+				mode := rest
+				content := ""
+				if idx := strings.IndexByte(rest, ' '); idx > 0 {
+					mode = rest[:idx]
+					content = strings.TrimSpace(rest[idx+1:])
+				}
+				body := fmt.Sprintf(`{"mode":%q,"content":%q}`, mode, content)
+				d, _ := rc.DoAPI("POST", "/api/v1/persona", body)
+				printJSON(out, d)
+			} else {
+				d, _ := rc.DoAPI("GET", "/api/v1/persona", "")
+				printJSON(out, d)
+			}
+		} else {
+			state.Send(cmd)
+		}
+		return true
+
 	case cmd == "/runtime":
 		if rc := state.RemoteConn(); rc != nil {
 			d, _ := rc.DoAPI("GET", "/api/v1/runtime", "")