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>

internal/version/version.go

@@ -1,11 +1,33 @@
 package version
 
+import (
+	"fmt"
+	"runtime"
+)
+
 const (
 	Name    = "muyue"
 	Version = "0.3.2"
 	Author  = "La Légion de Muyue"
 )
 
+var (
+	// BuildDate is set at build time
+	BuildDate = ""
+)
+
 func FullVersion() string {
 	return Name + " v" + Version
 }
+
+// FullInfo returns full version information.
+func FullInfo() string {
+	info := fmt.Sprintf("%-12s %s\n", "Version:", Version)
+	info += fmt.Sprintf("%-12s %s\n", "Author:", Author)
+	info += fmt.Sprintf("%-12s %s\n", "Go:", runtime.Version())
+	info += fmt.Sprintf("%-12s %s\n", "Platform:", runtime.GOOS+"/"+runtime.GOARCH)
+	if BuildDate != "" {
+		info += fmt.Sprintf("%-12s %s\n", "Build:", BuildDate)
+	}
+	return info
+}