ux: answer follow-up comments by default

[toadaid-agent0]

Toadgang UX: follow-up questions in the same Issue should be answered naturally.

Change:

• issue_comment triggers scribe-reflection for normal human comments (no need to type awaken or mention Agent1)
• skips obvious low-signal acknowledgements (thanks/gm/ok) to reduce noise
• loop guards + cooldown remain
• docs updated to match