feat: add plugin brand assets

[yourkase-chaehyun]

Summary

• add official PlanetScale logo marks for plugin composer and catalog surfaces
• provide a white dark-mode variant
• include brand assets in release archives

Validation

• verified SVG checksums against the assets published at https://planetscale.com/brand
• parsed the plugin manifest and release workflow
• validated both SVG files with xmllint
• built the release archive locally and confirmed the manifest and assets are included
• ran git diff --check

Note

The generic Codex plugin validator reports pre-existing findings for the repository’s submodule-backed skill layout. This change does not modify skill loading.

[SimeonGriggs]

Thanks for this — the brand assets and manifest wiring look good.

main requires GitHub-verified commit signatures. The commit on this PR is SSH-signed, but GitHub reports unknown_key because the signing key is not registered on the GitHub account. We are not adding outside collaborators to the org just to satisfy that rule.

I have recreated the same change on a maintainer branch with a verified signature: #5

Closing this PR in favor of that one. Credit remains yours via Co-authored-by.