fix(api): restrict fallback note to string-typed JSON values

Only emit note in listAuthFilesFromDisk when the JSON value is actually
a string (gjson.String), matching the synthesizer/buildAuthFileEntry
behavior. Non-string values like numbers or booleans are now ignored
instead of being coerced via gjson.String().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/api/handlers/management/auth_files.go

@@ -342,7 +342,7 @@ func (h *Handler) listAuthFilesFromDisk(c *gin.Context) {
 						}
 					}
 				}
-				if nv := gjson.GetBytes(data, "note"); nv.Exists() {
+				if nv := gjson.GetBytes(data, "note"); nv.Exists() && nv.Type == gjson.String {
 					if trimmed := strings.TrimSpace(nv.String()); trimmed != "" {
 						fileData["note"] = trimmed
 					}