chore: remove dead code (packages, functions, types, constants)

Remove 5 unused packages (daemon, preview, proxy, workflow) and dead
symbols across 7 files: orchestrator workflow engine, skills Target type
and Update(), LSP config generation, installer SetupPrompt(), unexported
desktop options, and version License/Prerelease. Total: -1453 lines.

internal/version/version.go

@@ -4,15 +4,8 @@ const (
 	Name    = "muyue"
 	Version = "0.2.1"
 	Author  = "La Légion de Muyue"
-	License = "MIT"
 )
 
-var Prerelease string
-
 func FullVersion() string {
-	v := Name + " v" + Version
-	if Prerelease != "" {
-		v += "-" + Prerelease
-	}
-	return v
+	return Name + " v" + Version
 }