Add origin_app to APActivity — apps only process their own activities

Each app's EventProcessor now filters by origin_app so apps don't steal
each other's pending activities. emit_activity() and publish_activity()
auto-detect the app name from Quart's current_app.

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

alembic/versions/o5m3j9k1l2_add_origin_app_column.py

@@ -0,0 +1,26 @@
+"""Add origin_app column to ap_activities
+
+Revision ID: o5m3j9k1l2
+Revises: n4l2i8j0k1
+Create Date: 2026-02-22
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "o5m3j9k1l2"
+down_revision = "n4l2i8j0k1"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "ap_activities",
+        sa.Column("origin_app", sa.String(64), nullable=True),
+    )
+    op.create_index("ix_ap_activity_origin_app", "ap_activities", ["origin_app"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_ap_activity_origin_app", table_name="ap_activities")
+    op.drop_column("ap_activities", "origin_app")