feat(pr-review): score confidence on 1 to 10 so clean reviews read safe - #1276

🟢 Confidence 4/5 · likely safe to merge
Self-contained rescale with matching tests; the migration's 1 AND 5 guard is the one spot that depends on the deploy ordering.
_{quality 100/100 · no findings · tests covered · risk medium}

Rescales PR review confidence from 1–5 to 1–10 with whole-point deductions, matching caps, a recalibrated prompt and a migration that doubles stored values. Contained and tested; safe to merge in the same deploy as the migration.

• confidencePrReview scores 1–10: whole-point deductions, caps at 2/4/6/8
• Check conclusion is success from 7 through prReviewConfidenceTone, was 4
• Comment, check title and web UI now render /10
• New migration doubles stored report_json.confidence from 1–5 to 2–10

Fixed since the last review

• ✅ F1 · Migration doubles confidence with no upper bound

_{cf2d749 · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}