feat(memory): add registerMemoryCommand for mosaic memory CLI surface

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>

packages/memory/src/index.ts

@@ -1,4 +1,5 @@
 export { createMemory, type Memory } from './memory.js';
+export { registerMemoryCommand } from './cli.js';
 export {
   createPreferencesRepo,
   type PreferencesRepo,