Fix blog: add page_configs migration, fix stale cart reference in ghost_sync

- Add 0003_add_page_configs.py migration to create table in db_blog
- Fix ghost_sync.py: fetch_data("cart", "page-config-ensure") → "blog"

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

blog/alembic/versions/0003_add_page_configs.py

@@ -0,0 +1,44 @@
+"""Add page_configs table — moved from cart service to blog.
+
+Revision ID: blog_0003
+Revises: blog_0002
+Create Date: 2026-02-27
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "blog_0003"
+down_revision = "blog_0002"
+branch_labels = None
+depends_on = None
+
+
+def _table_exists(conn, name):
+    result = conn.execute(sa.text(
+        "SELECT 1 FROM information_schema.tables WHERE table_schema='public' AND table_name=:t"
+    ), {"t": name})
+    return result.scalar() is not None
+
+
+def upgrade():
+    if _table_exists(op.get_bind(), "page_configs"):
+        return
+
+    op.create_table(
+        "page_configs",
+        sa.Column("id", sa.Integer, primary_key=True, autoincrement=True),
+        sa.Column("container_type", sa.String(32), nullable=False, server_default=sa.text("'page'")),
+        sa.Column("container_id", sa.Integer, nullable=False),
+        sa.Column("features", sa.JSON, nullable=False, server_default="{}"),
+        sa.Column("sumup_merchant_code", sa.String(64), nullable=True),
+        sa.Column("sumup_api_key", sa.Text, nullable=True),
+        sa.Column("sumup_checkout_prefix", sa.String(64), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+    )
+
+
+def downgrade():
+    op.drop_table("page_configs")

blog/bp/blog/ghost/ghost_sync.py

@@ -248,10 +248,10 @@ async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[
     finally:
         sess.autoflush = old_autoflush
 
-    # Auto-create PageConfig for pages (lives in db_cart, accessed via internal API)
+    # Auto-create PageConfig for pages (blog now owns this table)
     if obj.is_page:
         await fetch_data(
-            "cart", "page-config-ensure",
+            "blog", "page-config-ensure",
             params={"container_type": "page", "container_id": obj.id},
             required=False,
         )