generate_db: add by_sha256 index for O(1) variant lookup.
verify: _find_best_variant uses indexed sha256 instead of O(n) scan.
validation: check_file_validation returns (reason, emulators) tuple,
attributing mismatch only to emulators whose check actually failed.
beetle_psx: remove incorrect size field for ps1_rom.bin (code does
not validate size, swanstation is sole size authority).
Dolphin computes adler32 on byte-swapped (16-bit) data, not raw
file bytes. Add adler32_byteswap flag to dolphin/primehack/ishiiruka
profiles and support it in validation.py.
Reduces hash mismatch discrepancies from 18 to 2.
Run ruff check --fix: remove unused imports (F401), fix f-strings
without placeholders (F541), remove unused variables (F841), fix
duplicate dict key (F601).
Run isort --profile black: normalize import ordering across all files.
Run ruff format: apply consistent formatting (black-compatible) to
all 58 Python files.
3 intentional E402 remain (imports after require_yaml() must execute
after yaml is available).
