isSvgAsset function
Returns true when value points to a Flutter asset SVG.
Two conditions must hold: the value ends with .svg (case-insensitive) and
it is not a remote (http/https) URL.
Implementation
bool isSvgAsset(String? value) {
final lower = value?.trim().toLowerCase();
if (lower == null) return false;
return lower.endsWith('.svg') && !lower.startsWith('http');
}