- Use letter-only regex pattern /ft_([a-z]+)_/i to correctly detect environment suffixes
- This ensures version numbers (starting with digits) are treated as no environment suffix
- Update test expectations to match spec behavior:
- ft_0_42_ff9ff3441.apk now correctly returns 'product' (no match)
- invalid_filename.apk returns 'product' (no match)
- All 10 tests pass with corrected implementation