[Improve] Add prompt starters to Discord help

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Added three copyable task starters to the existing Discord /help response.
• Updated the /new request description to point users to those starters.
• Covered both the registered command metadata and complete help content with focused tests.

Why this change was made

Recurring agent instructions often live in separate scratch files. Surfacing adaptable starters inside Discord keeps that guidance in the team workflow where tasks are already launched, without adding a standalone prompt-management surface.

Impact

Discord users can discover, adapt, and launch common Roomote task patterns directly from /help and /new. Task routing, prompt persistence, and other communication providers are unchanged.

[roomote-community]

No code issues found. See task

_{Reviewed 66897d7}