Embed cl-sanitize-html instead of using submodule

Fixes CI build failure - submodules not checked out by default.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Anthony Green2025-12-26 08:34:25 -0500 725f5cc3d0bef8e0e26e1cdce24192743ddb07a4
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>