fix: LLM 工具循环 400、中断消息注入、ConPTY 终端支持

- agent: 工具轮请求尾部补 user 占位(zen 网关强制),tool 消息正确配对
- agent: 工具提醒/中断以 system 角色注入并带 [中断消息] 前缀,不进用户履历;系统提示词说明中断消息格式
- agentcli: 基于 ConPTY 的交互式终端(ptywin fork),terminal_create/read/write/resize/close/watch
- webui: server 输出通道适配器(保留 reasoning_content/disable_thinking)
- GUI: 沉浸式标题栏、icon 圆角重制、mascot 等打磨

internal/plugins/webui/handler_test.go

@@ -632,13 +632,13 @@ func TestSettingsAPIFlow(t *testing.T) {
 		if !strings.Contains(html, "settings-layout") {
 			t.Fatal("HTML should contain settings-layout class")
 		}
-		if !strings.Contains(html, "settings-sidebar") {
-			t.Fatal("HTML should contain settings-sidebar class")
+		if !strings.Contains(html, "settings-tabs") {
+			t.Fatal("HTML should contain settings-tabs class")
 		}
 		if !strings.Contains(html, "saveSetting") {
 			t.Fatal("HTML should contain saveSetting JS function")
 		}
-		if !strings.Contains(html, "api('/settings'") {
+		if !strings.Contains(html, `api("/settings"`) {
 			t.Fatal("HTML should call api('/settings')")
 		}
 	})