feat: 添加流式输出动画效果

- 添加 spinner 组件，使用 bubbletea v2 的 MiniDot 动画
- 用户输入后显示思考中动画
- 第一个 token 返回后显示思考完成
- 流式输出完成后添加空行分隔

cmd/hxclaw/internal/spinner.go

@@ -0,0 +1,90 @@
+package internal
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"charm.land/bubbles/v2/spinner"
+	"charm.land/lipgloss/v2"
+)
+
+type SpinnerState int
+
+const (
+	StateThinking SpinnerState = iota
+	StateAnswering
+	StateDone
+)
+
+type Spinner struct {
+	text    string
+	state   SpinnerState
+	spinner spinner.Model
+	stopCh  chan struct{}
+	doneCh  chan struct{}
+}
+
+func NewSpinner(text string) *Spinner {
+	s := spinner.New(
+		spinner.WithSpinner(spinner.MiniDot),
+		spinner.WithStyle(lipgloss.NewStyle().Foreground(lipgloss.Color("243"))),
+	)
+	return &Spinner{
+		text:    text,
+		state:   StateThinking,
+		spinner: s,
+		stopCh:  make(chan struct{}),
+		doneCh:  make(chan struct{}),
+	}
+}
+
+func (s *Spinner) Start() {
+	go s.run()
+	s.tick()
+}
+
+func (s *Spinner) Update(text string) {
+	s.text = text
+	s.state = StateAnswering
+}
+
+func (s *Spinner) Stop() {
+	close(s.stopCh)
+	<-s.doneCh
+}
+
+func (s *Spinner) tick() {
+	msg := s.spinner.Tick()
+	if msg, ok := msg.(spinner.TickMsg); ok {
+		s.spinner, _ = s.spinner.Update(msg)
+	}
+}
+
+func (s *Spinner) run() {
+	defer close(s.doneCh)
+
+	ticker := time.NewTicker(time.Second / 12)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			s.tick()
+			s.render()
+		case <-s.stopCh:
+			s.clear()
+			return
+		}
+	}
+}
+
+func (s *Spinner) render() {
+	fmt.Printf("\r%s %s", s.spinner.View(), s.text)
+	os.Stdout.Sync()
+}
+
+func (s *Spinner) clear() {
+	fmt.Printf("\r%s 思考完成.\n", s.spinner.View())
+	os.Stdout.Sync()
+}