Add the chihuahua runner

[Kyome22]

Pull Request

Type of Change

• Add a new runner
• Fix or improve an existing runner
• Other (site, docs, tooling)

Runner Summary

Chihuahua — a runner featuring a chihuahua character.

Checklist for Adding a Runner

• All frames are PNG files named <runner-name>-frame-<N>.png (numbered from 0), with a height of exactly 36px, a width between 10px and 100px, and all frames share the same size.
• The zip contains only the frames — no .DS_Store, __MACOSX/, or ._* entries.
• The runner is my original work, or I hold the rights to it, and I consent to its distribution under this repository's license (Apache-2.0).
• The runner does NOT contain third-party intellectual property (e.g., Pokémon, Mario, or other copyrighted/trademarked characters).
• Files are placed at runners/<runner-name>/ as <runner-name>-frames.zip, metadata.json, and preview.png.
• runners/manifest.json includes the new runner name, following the existing ordering of the list.
• metadata.json contains the correct displayName and author.
• preview.png is an animated PNG (APNG), 36px tall, at most 100px wide, and animates correctly.
• I have read CONTRIBUTING.md and followed the steps described there.