Adds mosaic memory CLI with four subcommands: search, stats,
insights list, and preferences list. Commands accept --db flag
(or MEMORY_DB_URL/DATABASE_URL env) to connect to pgvector or
keyword adapter. Smoke tests verify command wiring without DB.
Task: CU-05-04
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>