Add optional face alignment

[leblancfg]

Summary

• Add opt-in Cropper(align=True) support that uses YuNet eye landmarks to level slightly tilted faces before cropping.
• Add autocrop --align and keep default crop behavior unchanged.
• Preserve alpha-channel handling, support no-resize aligned crops, and skip alignment when estimated roll exceeds the guard.
• Document alignment behavior and limits.

Fixes #212

Verification

• uv run pytest tests/test_autocrop.py tests/test_cli.py
• just lint
• just test
• Smoke: uv run autocrop tests/data/obama.jpg --align > aligned.jpg produced a valid 500x500 JPEG.