feat(memory): review feedback quorum before promotion

**Context:** ROADMAP.md → Memory security → Review feedback quorum
**Related:** #27

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## Component

Agent (Python runtime)

## Describe the feature

Promote review-derived rules to **persistent memory** only after **corroboration**—e.g. pattern seen across trusted reviewers and multiple PRs—reducing single-comment poisoning.

## Use case

One malicious or mistaken review comment should not become a permanent repo rule. Teams want consensus before agent behavior changes.

## Proposed solution

1. Staging area for extracted rules (pending quorum).
2. Quorum config: min reviewers, min PRs, trusted reviewer list.
3. Promote to semantic memory when threshold met; else expire.
4. Operator API to force-promote or reject pending rules.

## Other information

- Complements **Review feedback memory loop** (#27).
- Design context: `docs/design/MEMORY.md`.

- [ ] This might be a breaking change

Inizia da docs/design/MEMORY.md e dalla sezione “Memory security” di ROADMAP.md, quindi esamina la issue correlata #27 per il contesto esistente sul memory-loop. Il lavoro è completato quando il design e l’implementazione coprono lo staging delle regole in sospeso, soglie di corroborazione configurabili, promozione o scadenza e azioni dell’operatore di force-promote o reject.

Scritto dal modello di indicizzazione a partire dal testo della issue.