Decouple `ai-reaction` emoji from status comment

[strawgate]

When ai-reaction: eyes is set, the workflow both adds a reaction emoji to the trigger and posts a "started/completed" status comment.

It might be nice to separate the reaction from the status comment, perhaps adding a status-comment field to independently control the comment:

ai-reaction: eyes          # Adds 👀 reaction
status-comment: false       # No "started/completed" comment

or maybe adding an ai-reaction of eyes-only or something similar.

Alternatively, it might be nice to have a setting on add-comment where it will update the "ai-reaction" tracking comment instead of posting a new one.

[pelikhan]

Copilot decouple both as described in the issue.