ci(trunk): add code quality checks

[ss-o]

Summary

• Add Trunk configuration for zunit with actionlint, yamllint, markdownlint, prettier, gitleaks, and git-diff-check.
• Add a Trunk caller workflow using the refreshed org-level reusable workflow from ci(trunk): refresh reusable workflow .github#404.
• Remove the deprecated Trunk upload job/token path from the caller workflow.
• Tune the initial formatter/linter baseline so Trunk can run in all-files CI mode without broad legacy-doc rewrites.
• Apply the minimal README formatting cleanup required by the new formatter baseline.

Closes #6.

Verification

• trunk check --all --no-fix --no-progress → ✔ No issues
• git diff --check
• YAML parse for .trunk/trunk.yaml, .trunk/configs/*.yaml, .github/workflows/trunk-check.yml
• ./build.zsh >/dev/null && PATH="$tmpbin:$PATH" ./zunit --tap tests → 108/108 passing
• GitHub PR checks after ci(trunk): refresh reusable workflow .github#404 merged:
  • Trunk Code Quality / Trunk Code Quality → pass
  • zsh-n → pass
  • zunit → pass

[Copilot]

Pull request overview

Adds a Trunk-based code quality CI pipeline to the zunit repository, configuring conservative formatters/linters (actionlint, yamllint, markdownlint, prettier, gitleaks, git-diff-check) and wiring them to the org-level reusable Trunk workflow. Minimal README cleanup is included to satisfy the new formatter baseline.

Changes:

• Introduce .trunk/ configuration (trunk.yaml, yamllint, markdownlint, gitignore) and a .prettierignore baseline.
• Add .github/workflows/trunk-check.yml invoking the shared z-shell/.github Trunk workflow on push/PR/schedule.
• Apply minor README formatting to comply with the new formatter rules.

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
README.md	Reformat code block indentation, remove a blank line, and switch a * list marker to -.
.trunk/trunk.yaml	Define Trunk CLI version, enabled/disabled linters, runtimes, and actions.
.trunk/configs/.yamllint.yaml	Yamllint baseline extending default with a few relaxed rules.
.trunk/configs/.markdownlint.yaml	Markdownlint baseline disabling a number of rules.
.trunk/.gitignore	Ignore Trunk local state directories.
.prettierignore	Exclude legacy docs and .travis.yml from Prettier.
.github/workflows/trunk-check.yml	Caller workflow delegating to the org reusable Trunk workflow.

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