feat(auth): add PostgreSQL session schema

[rd-code-23]

Summary

• add the connect-pg-simple-compatible PostgreSQL session table through Drizzle
• add primary-key lookup and expiration-cleanup indexes
• generate and track the initial SQL migration and Drizzle metadata
• organize database schemas into feature-focused modules
• reconcile the concrete session-store shape and cleanup behavior with the database documentation

Why

Server-side authentication needs a durable, migration-owned PostgreSQL session store before session middleware can be configured. Runtime table creation remains disabled by design.

Validation

• pnpm --filter @goforlift/api test — 11 tests passed
• pnpm --filter @goforlift/api typecheck
• pnpm --filter @goforlift/api lint
• targeted Prettier checks
• drizzle-kit check
• Drizzle generation reports no schema changes after the organization refactor
• git diff --check

A clean-database migration application was not run because Docker/PostgreSQL is not installed in the execution environment.

Closes #6