feat: support webp as a first-class output format

[alsi-lawr]

• I have read CONTRIBUTING.md.
• I have created a discussion that was approved by a maintainer (for new features). See Add WebP output support #50 and feat: support webp #60

Closes #50
Supersedes #60

Summary

Adds animated WebP output support:

Output out.webp

Uses:

-vcodec libwebp_anim
-pix_fmt yuva420p
-quality 100
-compression_level 3
-lossless 0
-loop 0
-an

WebP output is significantly smaller than equivalent GIFs while preserving animation and alpha (used for rounded corners).

Fixes vs #60

• Uses libwebp_anim (correct encoder for animation)
• Uses -quality instead of unused -crf
• Removes -b:v 0 (not meaningful for WebP)
• Uses yuva420p to preserve alpha
• Adds -compression_level to control encode time

Verification

Built locally and rendered from the same tape:

Output webp-smoke.gif
Output webp-smoke.webp

Confirmed:

• WebP renders and loops correctly
• Alpha works (rounded corners preserved)
• Timing matches GIF/WebM
• File size is much smaller than GIF
• Existing GIF/WebM outputs unchanged

WebP output (~19.2 KiB) vs GIF (~24.8 KiB) from the same recording.

Note

I've also migrated neofetch -> fastfetch because neofetch is dead. The good news is that now the fastfetch tape is more reproducible.