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

backend/src/v1/auth/router.py

@@ -73,13 +73,14 @@ async def create_email_session(
     )
     result = await service.create_email_session(payload)
     points_service = PointsService(repository=PointsRepository(session))
-    await points_service.grant_register_bonus_if_eligible(
+    bonus_result = await points_service.grant_register_bonus_if_eligible(
         user_id=UUID(result.user.id),
         user_email=result.user.email,
     )
     notification_service = NotificationService(NotificationRepository(session))
-    linked_count = await notification_service.link_published_notifications_to_user(
-        user_id=UUID(result.user.id)
+    linked_count = await notification_service.link_notifications_for_registered_user(
+        user_id=UUID(result.user.id),
+        is_first_registration=bonus_result.is_first_registration,
     )
     await session.commit()
     logger.info(

backend/src/v1/notifications/repository.py

@@ -9,6 +9,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from models.notification import Notification
 from models.user_notification import UserNotification
+from schemas.enums import NotificationTargetMode
 
 
 class NotificationRepository:
@@ -116,13 +117,24 @@ class NotificationRepository:
     async def commit(self) -> None:
         await self._session.commit()
 
-    async def link_published_notifications_to_user(self, *, user_id: UUID) -> int:
+    async def link_notifications_for_registered_user(
+        self, *, user_id: UUID, is_first_registration: bool
+    ) -> int:
+        target_modes: list[NotificationTargetMode]
+        if is_first_registration:
+            target_modes = [
+                NotificationTargetMode.NEW_USERS,
+                NotificationTargetMode.ALL_USERS,
+            ]
+        else:
+            target_modes = [NotificationTargetMode.ALL_USERS]
         notification_ids = list(
             (
                 await self._session.execute(
                     select(Notification.id).where(
                         Notification.status == "published",
                         Notification.deleted_at.is_(None),
+                        Notification.target_mode.in_(target_modes),
                     )
                 )
             )
@@ -136,8 +148,8 @@ class NotificationRepository:
             insert(UserNotification)
             .values(
                 [
-                    {"user_id": user_id, "notification_id": notification_id}
-                    for notification_id in notification_ids
+                    {"user_id": user_id, "notification_id": nid}
+                    for nid in notification_ids
                 ]
             )
             .on_conflict_do_nothing(index_elements=["user_id", "notification_id"])

backend/src/v1/notifications/service.py

@@ -123,9 +123,11 @@ class NotificationService:
             await self._repository.commit()
         return updated_count
 
-    async def link_published_notifications_to_user(self, *, user_id: UUID) -> int:
-        return await self._repository.link_published_notifications_to_user(
-            user_id=user_id
+    async def link_notifications_for_registered_user(
+        self, *, user_id: UUID, is_first_registration: bool
+    ) -> int:
+        return await self._repository.link_notifications_for_registered_user(
+            user_id=user_id, is_first_registration=is_first_registration
         )
 
 

backend/src/v1/points/service.py

@@ -61,6 +61,7 @@ class RegisterBonusResult:
     amount: int
     balance_after: int
     event_id: str
+    is_first_registration: bool = False
 
 
 @dataclass(frozen=True)
@@ -122,14 +123,17 @@ class PointsService:
         account = await self._repository.get_or_create_user_points_for_update(
             user_id=user_id
         )
-        if claim is not None and claim.balance_snapshot is not None:
-            account.balance = max(int(claim.balance_snapshot), 0)
-            account.version = int(account.version) + 1
+        if claim is not None:
+            is_first_registration = claim.first_user_id_snapshot is None
+            if claim.balance_snapshot is not None:
+                account.balance = max(int(claim.balance_snapshot), 0)
+                account.version = int(account.version) + 1
             return RegisterBonusResult(
                 granted=False,
                 amount=0,
                 balance_after=int(account.balance),
                 event_id=event_id,
+                is_first_registration=is_first_registration,
             )
 
         claimed = await self._repository.claim_register_bonus(
@@ -144,6 +148,7 @@ class PointsService:
                 amount=0,
                 balance_after=int(account.balance),
                 event_id=event_id,
+                is_first_registration=False,
             )
 
         balance = int(account.balance)
@@ -197,6 +202,7 @@ class PointsService:
             amount=bonus_points,
             balance_after=int(account.balance),
             event_id=event_id,
+            is_first_registration=True,
         )
 
     async def ensure_run_points_available(