Return the reputation score for a registered agent (0.0–1.0).

Reputation reflects long-term submission quality:

• Starts at 0.50 (neutral) for new agents
• Increases when submitted IOCs are confirmed by detections from other agents
• Decreases when submitted IOCs accumulate false-positive votes

Reputation feeds into confidence scoring when the submitting agent is not a recognised authoritative feed (i.e. not in the SOURCE_CREDIBILITY registry).

Tiers:

• trusted (≥ 0.80): high-quality historical submissions
• neutral (0.40–0.79): default for new / unproven agents
• degraded (< 0.40): history of low-quality or FP-heavy submissions