Add a Vector-Backed Semantic Memory Layer for Familiars

OpenCoven already has a strong local runtime foundation: project-scoped sessions, familiar identity, tool access, PTY supervision, event logs, and SQLite-backed persistence. A valuable next layer would be an optional semantic memory backend for familiars. Suggested architecture:

• Keep SQLite as the authoritative local store for sessions, events, logs, project metadata, and familiar records.
• Add a sidecar “memory vault” service for semantic retrieval.
• Support endpoints such as /query, /learn, /upload, /stats, and /health.
• Store chunked memories, embeddings, tags, source metadata, and uploaded documents.
• Let familiars query this memory before acting, so they can retrieve relevant prior decisions, project context, docs, user preferences, and historical work.
• Keep it local-first by default, but allow network-visible deployment over private networks like Tailscale for trusted multi-agent/team setups.

This would make OpenCoven’s persistent agents feel much more durable: not just resumable sessions, but familiars with long-term, searchable institutional memory.