fix(attach): address review bot feedback on warnings and footer
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- Suppress the "review prompt will be empty" warning when a pending-review marker's ReviewPromptOverride supplies the prompt; the general "no prompts parsed" warning still fires.
- Omit the footer token segment when the total is zero (not just nil), so it never renders "0 tokens" — matches the turns guard and the helper's doc.
- Truncate the amend-failure stderr note to the error's first line via the existing firstLine helper, keeping the full multi-line git output in the debug log only.
Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com Entire-Checkpoint: a548a19a0542
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