`optimize --target-size` — size-targeted compression

[gfargo]

Binary-search the quality parameter to hit a target file size.

localpress optimize 123 --target-size 100kb
localpress optimize --unoptimized --target-size 200kb --apply

Useful for hero images with strict performance budgets (e.g. "this image must be under 100KB for Core Web Vitals").

Implementation:

• Binary search on quality parameter (1-100)
• Encode at mid-quality, check size, adjust
• Stop when within 5% of target or after 8 iterations
• Report the final quality used in the output