feat(markdown-to-slack-mrkdwn): add action

[domasx2]

Summary

New composite action that converts CommonMark markdown to Slack mrkdwn (the syntax inside blocks[].text of a chat.postMessage payload). Wraps slackify-markdown, so callers can do this conversion without taking a third-party action dependency.

Bun-based, following the dependabot-auto-triage pattern. The 49-case upstream slackify-markdown test corpus runs in CI to lock in parity with the library.

Why

Grafana repos post release notifications to Slack and need a markdown → Slack mrkdwn conversion step. We were using 3d party action

PR description authored by Claude on Domas's behalf.

[Copilot]

Pull request overview

Adds a new Bun-based composite action markdown-to-slack-mrkdwn that wraps the slackify-markdown npm library to convert CommonMark to Slack mrkdwn, so Grafana repos can stop depending on a third-party action for Slack release-notification formatting. Follows the existing dependabot-auto-triage pattern (Bun runtime, composite action, workspace member, release-please-managed).

Changes:

• New action under actions/markdown-to-slack-mrkdwn/ (action.yml, src/index.ts, README, package.json, .bun-version) that reads INPUT_MARKDOWN, runs it through slackifyMarkdown, and writes the result to the text output via a GITHUB_OUTPUT heredoc.
• Test corpus port (49 cases) from upstream slackify-markdown plus null/undefined handling, executed with bun test.
• Workspace, root lockfile, and release-please manifest/config wired up for the new package.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
actions/markdown-to-slack-mrkdwn/action.yml	Composite action steps: setup-bun, install, run TS, emit text output via heredoc.
actions/markdown-to-slack-mrkdwn/src/index.ts	Thin wrapper exposing transform() and writing converted markdown to stdout.
actions/markdown-to-slack-mrkdwn/src/index.test.ts	Parity tests against upstream slackify-markdown corpus + nullish input.
actions/markdown-to-slack-mrkdwn/package.json	Workspace package metadata, scripts, slackify-markdown dep.
actions/markdown-to-slack-mrkdwn/README.md	Usage docs, inputs/outputs, embedding tips.
actions/markdown-to-slack-mrkdwn/.bun-version	Pins Bun 1.3.13 for setup-bun.
package.json	Adds new action to Bun workspaces.
bun.lock	Adds slackify-markdown and its mdast/micromark transitive deps.
release-please-config.json	Registers the new action for release-please.
.release-please-manifest.json	Initial 0.1.0 entry for the new package.

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