feat: add low-noise payoff-ranked findings

[ColumbusLabs]

Summary

• add presentation-only payoff-ranked --top N views across scan and adoption workflows
• make capped PR comments choose detailed findings by payoff without reordering canonical Action JSON
• document the recommended delta-only, capped low-noise adoption path

Verification

• npm run test:all
• npm run build
• repository self-scan with debtlens.self.config.json
• independent code review; all findings fixed and regression-tested

Closes #293
Closes #335

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