Add activity push notifications and registration patches

db/migrations/22_registration_badges.sql

@@ -0,0 +1,3 @@
+-- Assignment/backfill uses configurable dates in community_badges.reconcile at startup.
+CREATE UNIQUE INDEX IF NOT EXISTS idx_user_badges_registration_cohort
+    ON user_badges(user_id) WHERE badge_code IN ('alpha_tester', 'beta_tester', 'early_bird');