refactor(chat): deduplicate streaming code, add multi-conv, and XSS protection

- Add ChatEngine for deduplicated chat logic (handlers_chat/shell_chat)
- Add SendWithToolsStream for real-time streaming responses
- Add /help, /plan, /export, /model commands in Studio
- Fix XSS: sanitize HTML after markdown rendering
- Add ConversationStoreMulti for multi-conversation support
- Add Anthropic headers (x-api-key, anthropic-version)
- Add fallback logging when provider switch occurs
- Add API handler tests (handlers_test.go)
- Polish Studio: max-height 200px, word-break on tool args
- Update CLI version to show full info (version, go, platform)

🤖 Generated with Crush

Assisted-by: MiniMax-M2.5 via Crush <crush@charm.land>

cmd/muyue/commands/version.go

@@ -9,7 +9,7 @@ import (
 
 var versionCmd = &cobra.Command{
 	Use:   "version",
-	Short: "Print version",
+	Short: "Print version info",
 	RunE:  runVersion,
 }
 
@@ -18,6 +18,6 @@ func init() {
 }
 
 func runVersion(cmd *cobra.Command, args []string) error {
-	fmt.Printf("Muyue version %s\n", version.Version)
+	fmt.Print(version.FullInfo())
 	return nil
 }