feat: 增强聊天 UI 与终端配置

- 重构消息列表、思考块与工具调用块样式
- ChatContext 支持 agent 分段与 markdown 渲染优化
- 后端增加 PI 命令配置与 Web 终端改进
- 新增 run-backend.sh 启动脚本，忽略 backend/dist 构建产物

backend/internal/services/web_terminal.go

@@ -21,7 +21,7 @@ type terminalWSMessage struct {
 }
 
 // ServeWebTerminal attaches a PTY shell session to the websocket connection.
-func ServeWebTerminal(conn *websocket.Conn, workDir string) error {
+func ServeWebTerminal(conn *websocket.Conn, workDir, agentDir string) error {
 	abs, err := filepath.Abs(workDir)
 	if err != nil {
 		return fmt.Errorf("解析目录失败: %w", err)
@@ -34,15 +34,21 @@ func ServeWebTerminal(conn *websocket.Conn, workDir string) error {
 		return fmt.Errorf("不是有效目录: %s", abs)
 	}
 
+	envInject := map[string]string{
+		"TERM":      "xterm-256color",
+		"COLORTERM": "truecolor",
+	}
+	if agentDir != "" {
+		envInject["SPROUTCLAW_CODING_AGENT_DIR"] = agentDir
+		envInject["PI_CODING_AGENT_DIR"] = agentDir
+	}
+
 	ptmx, err := crosspty.Start(crosspty.CommandConfig{
-		Argv: defaultShellArgv(),
-		Dir:  abs,
-		Env:  os.Environ(),
-		EnvInject: map[string]string{
-			"TERM":      "xterm-256color",
-			"COLORTERM": "truecolor",
-		},
-		Size: crosspty.TermSize{Rows: 24, Cols: 80},
+		Argv:      defaultShellArgv(),
+		Dir:       abs,
+		Env:       os.Environ(),
+		EnvInject: envInject,
+		Size:      crosspty.TermSize{Rows: 24, Cols: 80},
 	})
 	if err != nil {
 		if err == crosspty.ErrConPTYNotSupported {