docs: add inline comments to product_integration_translations migration

database/migrations/20260227_000014_create_product_integration_translations.sql

@@ -2,6 +2,7 @@ CREATE TABLE IF NOT EXISTS product_integration_translations (
     id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
     product_id INT UNSIGNED NOT NULL,
     integration_id INT UNSIGNED NOT NULL,
+    -- NULL means "inherit from product_translations" for this integration
     name VARCHAR(255) NULL,
     short_description TEXT NULL,
     description LONGTEXT NULL,
@@ -29,6 +30,8 @@ SELECT
     pt.description,
     NOW(),
     NOW()
+-- NOTE: pcm.integration_id was added in migration 000007 (ALTER TABLE).
+-- If no product_channel_map rows have integration_id set, this inserts 0 rows (safe).
 FROM product_translations pt
 INNER JOIN product_channel_map pcm ON pcm.product_id = pt.product_id
 INNER JOIN integrations i ON i.id = pcm.integration_id