Add full-text contact search

[snbafana]

Summary

• add a maintained FTS5 document for each canonical contact
• search names, companies, handles, and current contact memories through cued contacts search
• keep the index current across contact, handle, and memory lifecycle changes

Validation

• pnpm exec vitest run src/db/database.test.ts src/cli-contacts-memory.test.ts
• pnpm typecheck
• pnpm exec biome check src/cli.ts src/cli-contacts-memory.test.ts src/db/database.ts src/db/migrations.ts