No CI workflow and no .coderabbit.yaml despite CLAUDE.md documenting a CodeRabbit process

[carochacs]

Problem

This repo has no .github/workflows/* CI config and no .coderabbit.yaml. Meanwhile the sibling slopsmith-plugin-editor repo has both: a ci.yml that runs pytest + node --test, and a .coderabbit.yaml that documents this repo's own conventions so CodeRabbit doesn't re-flag deliberate design decisions.

Splitscreen's own CLAUDE.md is one of the most detailed in the whole plugin ecosystem (module structure, panel lifecycle, follower/pop-out protocol, viz contract) — exactly the kind of subtle, deliberate-looking code that benefits most from a review bot primed with the right context, and from CI catching regressions given the size of screen.js (~5,550 lines per the editor's own CLAUDE.md scale, and this repo is comparably large).

Ask

Bring this repo's dev tooling in line with plugin-editor's pattern:

1. Add a ci.yml GitHub Actions workflow that runs this repo's test suite (see companion issue on test coverage — currently only one test file exists)
2. Add a .coderabbit.yaml documenting splitscreen-specific conventions from CLAUDE.md (e.g. the panel lifecycle contract, the sizeCanvases() call sites, the follower/pop-out BroadcastChannel protocol) so review comments don't re-litigate deliberate design
3. Add a short "Working with CodeRabbit" section to CLAUDE.md mirroring plugin-editor's

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Migrated from Maestro-Ltd/slopsmith-plugin-splitscreen#16.