agents: Implement Fact Checker Agent with temporal expiry and verification plugins

[rdwj]

Summary

Implement the Fact Checker Agent as a Kubernetes CronJob. Performs periodic verification of factual claims in memories against current state, processes temporal expiry via relevant_until, and supports pluggable verification backends. Uses mid-tier model for classification tasks.

Design reference

• planning/autonomous-curation-agents.md Section 5.3 (Fact Checker)

Scope

• Service identity and API key for fact-checker
• Calendar-aware expiry: auto-expire memories past relevant_until, flag approaching expiry (7-day window)
• Verification plugin architecture: VerificationPlugin ABC with can_verify() and verify() methods
• CalendarPlugin: check temporal claims against current date (ships first)
• Domain-scoped plugin routing: plugins declare which domains they handle
• Contradiction reporting for verified-false claims via memory(action="report")
• Metadata updates: metadata_.temporal_status (expired, expiring_soon, current)
• CronJob manifest, daily schedule
• RBAC: memory:read, memory:write:user (metadata only), memory:write:project, memory:write:campaign
• Multiple replicas OK (no singleton constraint, concurrent flagging is idempotent)

Dependencies

• schema: Add relevant_until column and temporal classification #282 (relevant_until schema)
• infra: Deploy Valkey to memoryhub-agents namespace #283 (Valkey deployment)
• agents: Build shared agent framework for authenticate/dequeue/process/report pattern #286 (shared agent framework)
• Tracking: Autonomous Curation Agents (epic tracker) #281