feat(subscriptions): migrate subscription management to merchant level and seed tiers

Move subscription create/edit from store detail (broken endpoint) to merchant
detail page with proper modal UI. Seed 4 subscription tiers (Essential,
Professional, Business, Enterprise) in init_production.py. Also includes
cross-module dependency declarations, store domain platform_id migration,
platform context middleware, CMS route fixes, and migration backups.

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

alembic/versions_backup/a2064e1dfcd4_add_cart_items_table.py

@@ -0,0 +1,67 @@
+"""add cart_items table
+
+Revision ID: a2064e1dfcd4
+Revises: f68d8da5315a
+Create Date: 2025-11-23 19:52:40.509538
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "a2064e1dfcd4"
+down_revision: Union[str, None] = "f68d8da5315a"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Create cart_items table
+    op.create_table(
+        "cart_items",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("vendor_id", sa.Integer(), nullable=False),
+        sa.Column("product_id", sa.Integer(), nullable=False),
+        sa.Column("session_id", sa.String(length=255), nullable=False),
+        sa.Column("quantity", sa.Integer(), nullable=False),
+        sa.Column("price_at_add", sa.Float(), nullable=False),
+        sa.Column("created_at", sa.DateTime(), nullable=True),
+        sa.Column("updated_at", sa.DateTime(), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["product_id"],
+            ["products.id"],
+        ),
+        sa.ForeignKeyConstraint(
+            ["vendor_id"],
+            ["vendors.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint(
+            "vendor_id", "session_id", "product_id", name="uq_cart_item"
+        ),
+    )
+
+    # Create indexes
+    op.create_index(
+        "idx_cart_session", "cart_items", ["vendor_id", "session_id"], unique=False
+    )
+    op.create_index("idx_cart_created", "cart_items", ["created_at"], unique=False)
+    op.create_index(op.f("ix_cart_items_id"), "cart_items", ["id"], unique=False)
+    op.create_index(
+        op.f("ix_cart_items_session_id"), "cart_items", ["session_id"], unique=False
+    )
+
+
+def downgrade() -> None:
+    # Drop indexes
+    op.drop_index(op.f("ix_cart_items_session_id"), table_name="cart_items")
+    op.drop_index(op.f("ix_cart_items_id"), table_name="cart_items")
+    op.drop_index("idx_cart_created", table_name="cart_items")
+    op.drop_index("idx_cart_session", table_name="cart_items")
+
+    # Drop table
+    op.drop_table("cart_items")