fix(ci): resolve CodeQL failures and suppress AI co-author trailers

[sanmak]

Summary

• Bump actions/checkout v4 → v6 across all workflows (ci, codeql, release) — supersedes build(deps): bump actions/checkout from 4 to 6 #8
• Bump github/codeql-action v3 → v4 — supersedes build(deps): bump github/codeql-action from 3 to 4 #7
• Fix CodeQL language from javascript-typescript to actions (repo has no JS/TS source code, causing the "Analyze" check to fail on both Dependabot PRs)
• Suppress AI co-author trailers in commit messages — adds explicit directive to the stage-and-commit skill ensuring commits are attributed solely to the system's git user unless commit.coAuthor is configured

Test plan

• Verify CodeQL "Analyze" check passes (no longer scanning for non-existent JS/TS)
• Verify CI checks pass (actions/checkout v6 compatible)
• Close build(deps): bump github/codeql-action from 3 to 4 #7 and build(deps): bump actions/checkout from 4 to 6 #8 as superseded after merge

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[Copilot]

Pull request overview

This PR updates ShipKit’s commit-message guidance to strictly control when a co-author trailer is added, and refreshes GitHub Actions workflows (checkout + CodeQL) to newer major versions / settings.

Changes:

• Tighten /commit + stage-and-commit instructions to forbid any co-author trailer unless commit.coAuthor is explicitly set to a non-null string in .shipkit.json.
• Add clearer examples for commit messages with/without commit.coAuthor.
• Update GitHub Actions workflows to use newer actions/checkout and github/codeql-action majors, and adjust CodeQL language configuration.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
skills/stage-and-commit.md	Clarifies when co-author trailers may be appended; adds examples.
commands/commit.md	Aligns /commit procedure with stricter co-author trailer rule.
.github/workflows/release.yml	Bumps checkout action major used during releases.
.github/workflows/codeql.yml	Switches CodeQL language to actions and bumps CodeQL/checkout action majors.
.github/workflows/ci.yml	Bumps checkout action major across CI jobs.
.claude/commands/skills/stage-and-commit.md	Mirrors the skills/ stage-and-commit guidance change for Claude.
.claude/commands/commands/commit.md	Mirrors the commands/ commit guidance change for Claude.