feat(notification): add target_mode enum constraint and merge register-notifications script

- Add NotificationTargetMode enum (new_users/exist_users/all_users/user_ids)
- Create Alembic migrations: drop duplicate indexes, add target_mode column
- Merge register-notifications.sh into dev-migrate.sh sync-notifications subcommand
- Shorten notification config path: static/notification/notifications -> static/notifications
- Update registration flow to dispatch notifications by target_mode
- Add is_first_registration to RegisterBonusResult for first-time user detection
- Remove dead code: link_published_notifications_to_user
- Update welcome_points.yaml to target new_users only
- Add 44 unit tests + 1 integration test, all passing

infra/scripts/dev-migrate.sh

@@ -6,12 +6,13 @@ ENV_FILE="$ROOT_DIR/.env"
 ENV_LOADER="$ROOT_DIR/infra/scripts/lib/env.sh"
 
 usage() {
-  echo "Usage: $0 {migrate|init-data|bootstrap}"
+  echo "Usage: $0 {migrate|init-data|sync-notifications|bootstrap}"
   echo ""
   echo "Commands:"
-  echo "  migrate     Run database migrations only"
-  echo "  init-data   Initialize seed data only"
-  echo "  bootstrap   Run migrations + init-data"
+  echo "  migrate             Run database migrations only"
+  echo "  init-data           Initialize seed data only"
+  echo "  sync-notifications  Sync static notification configs to DB"
+  echo "  bootstrap           Run migrations + init-data + sync-notifications"
   echo ""
   echo "Note: Requires redis service running (docker compose up -d redis)"
   exit 1
@@ -37,6 +38,11 @@ case "${1:-}" in
     echo "=== Running Init Data ==="
     PYTHONPATH=backend/src uv run python -m core.runtime.cli init-data
     ;;
+  sync-notifications)
+    shift
+    echo "=== Running Sync Notifications ==="
+    PYTHONPATH=backend/src uv run python -m core.runtime.cli sync-notifications "$@"
+    ;;
   bootstrap)
     echo "=== Running Bootstrap ==="
     PYTHONPATH=backend/src uv run python -m core.runtime.cli bootstrap