add persistant db with login_session chats and interactions, remove the localStorage

fix: async LLM calls and SESSIONS memory optimization (issue #11, #12)

admin: add interaction duration, show N/A for pending survey rating

feat: enforce questionId roundtrip in grade, add v2.2 tests, make participant_id nullable

add in-app survey, admin dashboard, and participant overview

embed participation id in the link, chagne the participation table structure

refactor: login_id to participant_id mapping, replace name/email auth

add PostgreSQL persistence for sessions and interaction metrics