chore(go): audit shared plugin helpers

Drop unused expandHome and standardizeJSONC, share the runtime base URL
validator between the guard and audit templates, and trim comments.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

cmd/elydora/plugins/legacy_hook_entries.go

@@ -2,8 +2,7 @@ package plugins
 
 import "strings"
 
-// extractElydoraScriptPath supports adapters that still use the legacy shared
-// command-hook shape. Provider-specific adapters should define exact ownership.
+// extractElydoraScriptPath reads the legacy shared command-hook shape.
 func extractElydoraScriptPath(hookArray any) string {
 	entries, _ := hookArray.([]any)
 	for _, entry := range entries {