Describe the local-auth E2E database and port in AGENTS.md

Assistant-model: Claude Opus 5.5
Assistant-workflow: inline
Assistant-verification: bun run ci passed: dprint, oxlint, tokens
Assistant-verification: manual source check passed: scripts/e2e.ts defines databases on 5433-5435 and e2e/local-auth.e2e.ts starts its app on 8791
Co-authored-by: Alex Lavaee <lavaman131@github.com>