fix: replace N+1 UPC query with SQL containment in normalization

- Add PostgreSQL JSONB containment (@>) query for match_by_upc
- Add SQLite LIKE fallback for test compatibility
- Update upc_variants column to JSONB with variant for cross-db support
- Add GIN index migration for upc_variants

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api/alembic/versions/009_add_gin_index_upc_variants.py

@@ -0,0 +1,38 @@
+"""Add GIN index on upc_variants and alter column to JSONB.
+
+Revision ID: 009_add_gin_index_upc_variants
+Revises: 008_create_domain_tables
+Create Date: 2026-04-14
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "009_add_gin_index_upc_variants"
+down_revision = "008_create_domain_tables"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.alter_column(
+        "normalized_products",
+        "upc_variants",
+        type_=sa.dialects.postgresql.JSONB(),
+        postgresql_using="upc_variants::jsonb",
+    )
+    op.create_index(
+        "ix_normalized_products_upc_variants_gin",
+        "normalized_products",
+        ["upc_variants"],
+        postgresql_using="gin",
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_normalized_products_upc_variants_gin", table_name="normalized_products")
+    op.alter_column(
+        "normalized_products",
+        "upc_variants",
+        type_=sa.JSON(),
+    )