Add memory tables to DB schema (preferences, insights with pgvector
embedding column, agent_logs, skills, summarization_jobs). Implement
PreferencesRepo (CRUD + upsert) and InsightsRepo (CRUD + semantic
search + relevance decay). Define VectorStore and EmbeddingProvider
interfaces for future provider abstraction. Wire MemoryModule into
gateway with REST endpoints at /api/memory/*.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
