Add support for mentioning channels by ID. e.g. <#C04A9JK5R3Z>

[nbarnett]

Similar to user mentions, Slack supports mentioning channels via their ID. For example <#C04A9JK5R3Z> will be transformed to #general. This PR adds the # prefix to the existing @ prefix in the regex for checking user mentions, so that the angle brackets don't get escaped. Test included.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7aa6c0b) to head (0f1c1d0).
Report is 1 commits behind head on master.

Additional details and impacted files

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[Copilot]

Pull Request Overview

This PR updates the mention parsing logic to also support channel mentions by ID, in addition to the existing user mention support.

• Updates regex patterns in src/slackify.js to include the '#' prefix.
• Adds a new test case for channel mention in test/slackify-markdown.test.js.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/slackify.js	Updated regex to handle both '@' and '#' prefixes
test/slackify-markdown.test.js	Added test to verify channel mention handling

Comments suppressed due to low confidence (1)

src/slackify.js:14

• The variable name 'isEndOfUserMention' is now used to check mentions that may include channels as well as users. Consider renaming it to a more inclusive name, such as 'isEndOfMention'.

      const isEndOfUserMention = Boolean(m.match(/<[@#][A-Z0-9]+$/));

[jsarafajr]

Thanks, will publish as new minor version today