Show per-app actor in follow notifications on Hub

Add app_domain to APNotification model and NotificationDTO so follow
notifications display "followed you on blog" instead of just "followed
you" when the follow targets a per-app actor.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/alembic/versions/w3u1q9r0s1_add_app_domain_to_notifications.py

@@ -0,0 +1,23 @@
+"""Add app_domain to ap_notifications.
+
+Revision ID: w3u1q9r0s1
+Revises: v2t0p8q9r0
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "w3u1q9r0s1"
+down_revision = "v2t0p8q9r0"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "ap_notifications",
+        sa.Column("app_domain", sa.String(30), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("ap_notifications", "app_domain")

shared/contracts/dtos.py

@@ -316,3 +316,4 @@ class NotificationDTO:
     from_actor_domain: str | None = None
     from_actor_icon: str | None = None
     target_content_preview: str | None = None
+    app_domain: str | None = None

shared/infrastructure/ap_inbox_handlers.py

@@ -253,6 +253,7 @@ async def handle_follow(
             actor_profile_id=actor_row.id,
             notification_type="follow",
             from_remote_actor_id=ra.id,
+            app_domain=app_domain,
         )
         session.add(notif)
 

shared/models/federation.py

@@ -422,6 +422,7 @@ class APNotification(Base):
     target_remote_post_id: Mapped[int | None] = mapped_column(
         Integer, ForeignKey("ap_remote_posts.id", ondelete="SET NULL"), nullable=True,
     )
+    app_domain: Mapped[str | None] = mapped_column(String(30), nullable=True)
     read: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default="false")
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now(),

shared/services/federation_impl.py

@@ -1620,6 +1620,7 @@ class SqlFederationService:
                 target_content_preview=preview,
                 created_at=notif.created_at,
                 read=notif.read,
+                app_domain=notif.app_domain,
             ))
         return items