Teach the skills how the tracker collaborates

[jserv]

Contributors keep receiving the same review requests, and the skills explained few of them. A new shared collaboration reference, read by both contribute and triage, records how work moves here: both maintainers' reviews bind, one change per pull request with review follow-ups kept in it, green CI before asking for review, how to answer a cubic finding, and what each short review request ("Fold similar commits", "Avoid ambiguous Refs #N", "Do more analysis and refinements.") asks for. Triage gains the acceptance comment and the dated reminder the maintainers use, with a pending reminder's deadline surviving a rescope. Its Closes/Refs and title pointers now go to CONTRIBUTING.md, where those rules live. The web and verify skills add the accessibility, editor light-theme, IME and browser-test points reviews keep raising.

The PR sweep now also counts the short hand-written "Rebase latest main branch and resolve conflicts." as a rebase request. It no longer asks again on a PR that already has one on its current head, and an earlier one can be hidden without a separate confirmation.

Validation: every relative link and anchor under .claude/skills/ resolves. pr-sweep.sh passes sh -n, commentflow and shfmt; shellcheck is not installed locally, so CI's lane is the first to run it. A live read-only sweep now lists #262's earlier long rebase request under hide and keeps its newest short one. scripts/test.sh does not cover .claude/. agy, codex and claude reviewed the diff, and each finding was checked against the cited thread or code before it was applied or rejected.

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Summary by cubic

Teaches the CodeTrial skills how the tracker collaborates, so contributors stop hitting review requests the skills previously left unexplained.

• Adds a shared collaboration reference, read by both the contribute and triage skills, covering who the maintainers are, one change per PR, green CI before asking for review, and what each short review request means.
• Gives triage the acceptance comment and dated-reminder shapes maintainers use; a pending reminder's deadline survives a rescope.
• Points triage's Closes/Refs and title rules at CONTRIBUTING.md instead of conventions.
• Adds accessibility, editor light-theme, IME, and browser-test points to the web and verify skills.
• Makes the PR sweep count the hand-written "Rebase latest main branch and resolve conflicts." as a rebase request, but only where main is the default branch; it no longer asks again on a PR that already has one and can hide an earlier one without a separate confirmation.
• The sweep now reads the failing job before attributing a check failure, and passes gh pr list an explicit --limit 1000 instead of stopping at 30.

^{Written for commit 5a1eb3f. Summary will update on new commits.}