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/rpc/client.go

@@ -73,16 +73,19 @@ type Client struct {
 // with the exit code when the subprocess terminates.
 func NewClient(piCmd string, piArgs []string, repoRoot, agentDir string, onExit func(int)) (*Client, error) {
 	if piCmd == "" {
-		return nil, fmt.Errorf("pi CLI command not specified (use --pi-cmd)")
+		return nil, fmt.Errorf("SproutClaw CLI command not specified (use --pi-cmd or --sproutclaw-cmd)")
 	}
 
-	// pi enters RPC mode via "--mode rpc"
+	// SproutClaw enters RPC mode via "--mode rpc"
 	args := append(append([]string{}, piArgs...), "--mode", "rpc")
 	cmd := exec.Command(piCmd, args...)
 	cmd.Dir = repoRoot
-	cmd.Env = append(os.Environ(), fmt.Sprintf("SPROUTCLAW_CODING_AGENT_DIR=%s", agentDir))
+	cmd.Env = append(os.Environ(),
+		fmt.Sprintf("SPROUTCLAW_CODING_AGENT_DIR=%s", agentDir),
+		fmt.Sprintf("PI_CODING_AGENT_DIR=%s", agentDir),
+	)
 
-	log.Printf("[sproutclaw-web] launching pi RPC: %s %s (cwd=%s)", piCmd, strings.Join(args, " "), repoRoot)
+	log.Printf("[sproutclaw-web] launching SproutClaw RPC: %s %s (cwd=%s agent-dir=%s)", piCmd, strings.Join(args, " "), repoRoot, agentDir)
 
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
@@ -115,7 +118,7 @@ func NewClient(piCmd string, piArgs []string, repoRoot, agentDir string, onExit
 		if cmd.ProcessState != nil {
 			code = cmd.ProcessState.ExitCode()
 		}
-		log.Printf("[sproutclaw-web] pi RPC exited, code=%d", code)
+		log.Printf("[sproutclaw-web] SproutClaw RPC exited, code=%d", code)
 		onExit(code)
 	}()