fix(ui): use accent bullet instead of "(active)" in model list

The `/models` command was showing model names with "(active)" suffix
which was noisy and cluttered the list.

Changed to use an accent-colored bullet (•) before the active model name
instead of a text suffix. This is:
- More visually distinct (color + symbol)
- Less cluttered (no trailing text)
- Consistent with the app's visual language

Example:
Before:  qwen3:8b (active)
After:   • qwen3:8b

Closes #165

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: cpcloud

internal/app/chat.go

@@ -388,7 +388,9 @@ func (m *Model) handleModelsListMsg(msg modelsListMsg) {
 	var b strings.Builder
 	for _, name := range msg.Models {
 		if name == current {
-			b.WriteString("  " + name + " (active)\n")
+			// Use accent-colored bullet to indicate active model.
+			marker := lipgloss.NewStyle().Foreground(accent).Render("• ")
+			b.WriteString(marker + name + "\n")
 		} else {
 			b.WriteString("  " + name + "\n")
 		}