new and improved sanitize method

[guycalledseven]

Fixes & Optimizations

✅ UTF-8 Transliteration

• Converts šđčć.png → sdc.png (removes accents & special characters)
• Uses transliterator_transliterate() (if available) or iconv() fallback.

✅ Handles Filename Length Properly

• Uses mb_substr() to safely trim multibyte characters.

✅ Removes Double Extensions

• Prevents filenames like file..png.

✅ Ensures a Safe Filename

• Removes dangerous characters.
• Keeps only ASCII, dots, dashes, and underscores.