fix(commands): use standard markdown for bold in command output

[sahil-tandon]

What this fixes/addresses

The channel-digest, draft-announcement, and standup commands tell the
assistant to format bold with a single asterisk (*text*), Slack's older
mrkdwn convention. Standard markdown reads a single asterisk (or underscore) as italic and
requires double asterisks for bold. So wherever the command output lands in a
standard-markdown surface, the intended bold renders as italic. That includes
markdown files and the Slack MCP server, which expects standard markdown
(so, for instance, draft-announcement writes a malformed-bold draft into Slack).

How I found it

I ran /slack:channel-digest and saved the output into a markdown file. The
digest's bold headers (the "Channel Digest" title and the #channel names)
showed up italic instead of bold. Tracing it to the command template, it emits
single-asterisk bold. Found the same pattern in draft-announcement
(which even explicitly says to use *bold* "not **bold**") and standup as well,
so this PR fixes all three. This also aligns the commands with the
slack-messaging skill, which already documents standard markdown (**bold**).

How to reproduce

1. Run /slack:channel-digest <channel> on main against any channel, and
   capture the output to a markdown file (or post it to Slack).
2. The headers come out as *...* and render italic.
3. On this branch, the same command emits **...** and renders bold.
4. draft-announcement behaves the same: it writes the announcement as a Slack
   draft, so the malformed bold shows up directly in Slack (see screenshots).

The fix

• commands/channel-digest.md — digest header lines to **...**
• commands/draft-announcement.md — formatting instruction to standard markdown
• commands/standup.md — standup header lines to **...**

Screenshots & verification

I verified end to end: created throwaway test channels, posted test messages, and ran
the affected commands both before and after the fix (reloading the plugin in
between). Before rendered italic; after rendered bold.

Markdown file (channel-digest)

• Before (single asterisk, renders italic):

• After (double asterisk, renders bold):

Slack draft (draft-announcement)

• Before (single asterisk, renders italic):

• After (double asterisk, renders bold):

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @sahil-tandon to sign the Salesforce Inc. Contributor License Agreement.

[WilliamBergamin]

Good find 💯 tested it on my end and this fixed the italic to bold issue

Thanks for your interest and contribution 🙏