feat(engagement): localize limits and streaks

Use reported user timezones for daily response limits, expose couple streak state and reminders, and improve swipe and live-drawing synchronization with focused tests and documentation.

apps/api/drizzle/0016_streak_reminder_preference.sql

@@ -0,0 +1,3 @@
+-- A shared streak only changes behaviour if somebody is told it is still open, so the
+-- evening at-risk nudge gets its own opt-out rather than riding on milestone celebrations.
+ALTER TABLE "notification_preferences" ADD COLUMN IF NOT EXISTS "streak_reminders_enabled" boolean NOT NULL DEFAULT true;