Add missing Alembic migration for user push columns and webmention table

The previous commit added notification_preference and push_subscriptions
columns to rb_user and a new rb_webmention table without migrations,
causing 502 on production.

remarkbox/scripts/alembic/versions/b7f3a2d1e8c9_add_push_notifications_and_webmentions.py

@@ -0,0 +1,45 @@
+"""add push notification columns to user and webmention table
+
+Revision ID: b7f3a2d1e8c9
+Revises: 896568b0752e
+Create Date: 2026-02-01 21:00:00.000000
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'b7f3a2d1e8c9'
+down_revision = '896568b0752e'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+from remarkbox.models.meta import UUIDType
+
+
+def upgrade():
+    # T10: push notification preferences on user
+    op.add_column('rb_user', sa.Column('notification_preference', sa.Unicode(length=5), server_default='email', nullable=False))
+    op.add_column('rb_user', sa.Column('push_subscriptions', sa.UnicodeText(), nullable=True))
+
+    # T7: webmention table
+    op.create_table(
+        'rb_webmention',
+        sa.Column('id', UUIDType, primary_key=True, index=True),
+        sa.Column('source', sa.Unicode(2048), nullable=False),
+        sa.Column('target', sa.Unicode(2048), nullable=False),
+        sa.Column('node_id', UUIDType, sa.ForeignKey('rb_node.id'), index=True, nullable=True),
+        sa.Column('verified', sa.Boolean(), default=False, nullable=False),
+        sa.Column('author_name', sa.Unicode(256), nullable=True),
+        sa.Column('author_url', sa.Unicode(2048), nullable=True),
+        sa.Column('content', sa.UnicodeText(), nullable=True),
+        sa.Column('created_timestamp', sa.BigInteger(), nullable=False),
+        sa.Column('updated_timestamp', sa.BigInteger(), nullable=False),
+    )
+
+
+def downgrade():
+    op.drop_table('rb_webmention')
+    op.drop_column('rb_user', 'push_subscriptions')
+    op.drop_column('rb_user', 'notification_preference')