Auto-skip when a triager has already left a similar comment

When a triager (any user with the triager role, including the bot itself) has already left a comment on a PR and the classifier would now propose a *similar* comment, **classify the action as `skip` automatically** rather than queuing the near-duplicate for human confirmation.

**Why:** today the human triager has to repeatedly dismiss "we already said this" proposals. It wastes attention and risks accidental duplicate posts when the operator clicks through too quickly.

### Open questions
- **Similarity definition:** exact rule-class match (same template / classifier rule fired before), keyword overlap, or embedding similarity? Rule-class match is the simplest and probably catches the bulk of duplicates.
- **Threshold knob** exposed to the user via config?
- **Logging:** silent skip, or a brief note in the progress output ("auto-skipped — same as existing triager comment by @user")?

Related but distinct: Issue for "repeat-triage avoidance when maintainer already engaged" — that is about *any* engagement; this one is about *similarity of the proposed comment*.