Add per-app ActivityPub actors via shared AP blueprint

Each AP-enabled app (blog, market, events, federation) now serves its
own webfinger, actor profile, inbox, outbox, and followers endpoints.
Per-app actors are virtual projections of the same ActorProfile/keypair,
scoped by APFollower.app_domain and APActivity.origin_app.

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

alembic/versions/t0r8n4o6p7_add_app_domain_to_ap_followers.py

@@ -0,0 +1,42 @@
+"""Add app_domain to ap_followers for per-app AP actors
+
+Revision ID: t0r8n4o6p7
+Revises: s9q7n3o5p6
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "t0r8n4o6p7"
+down_revision = "s9q7n3o5p6"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column(
+        "ap_followers",
+        sa.Column("app_domain", sa.String(64), nullable=True),
+    )
+    # Replace old unique constraint with one that includes app_domain
+    op.drop_constraint("uq_follower_acct", "ap_followers", type_="unique")
+    op.create_unique_constraint(
+        "uq_follower_acct_app",
+        "ap_followers",
+        ["actor_profile_id", "follower_acct", "app_domain"],
+    )
+    op.create_index(
+        "ix_ap_follower_app_domain",
+        "ap_followers",
+        ["actor_profile_id", "app_domain"],
+    )
+
+
+def downgrade():
+    op.drop_index("ix_ap_follower_app_domain", table_name="ap_followers")
+    op.drop_constraint("uq_follower_acct_app", "ap_followers", type_="unique")
+    op.create_unique_constraint(
+        "uq_follower_acct",
+        "ap_followers",
+        ["actor_profile_id", "follower_acct"],
+    )
+    op.drop_column("ap_followers", "app_domain")