Add optimize_alpha() function that sweeps hardware-friendly alpha
values to find the best DE threshold with normalized min-sum.
Add alpha-sweep CLI subcommand and --z/--cn-mode/--alpha options
to the full pipeline.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Thread cn_mode and alpha parameters through the entire DE pipeline:
de_cn_update_vectorized(), density_evolution_step(), run_de(),
compute_threshold(), and compute_threshold_for_profile().
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
