Adds user_preferences, user_consents, user_contexts and the tone /
tip_kinds_json columns on users. Backfills consent_given=1 rows into
user_consents as data:core; INSERT OR IGNORE keeps it idempotent and
respects later revocations.
Migration body moves to db/migrations.ts so tests can apply it to a
fresh in-memory handle without opening the prod DB on import.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
