feat: add graph_memory (Mnemograph)

[gdeyoung]

Plugin: Mnemograph (Graph Memory)

In-process knowledge graph for AI agents — entity extraction, relationship tracking, and recall enrichment. Zero external databases, zero network calls, runs entirely inside the agent using SQLite and asyncio.

• GitHub: https://github.com/gdeyoung/mnemograph
• Tags: memory, storage, tools, agents, workflow

Key Features

• Zero infrastructure: SQLite WAL + asyncio, no external DB or services required
• LLM-agnostic: Uses the agent's own utility model for extraction
• Safety-first: Circuit breaker, bounded queue, PII detection, hard latency budgets (50ms recall, 10ms injection)
• Self-maintaining: Auto-cleanup with orphan removal and VACUUM on health check
• Production-proven: 861 entities, 1,505 relationships in live single-agent deployment
• Framework-agnostic core: Hermes port planned