Add consignment_detail table for consignment inventory

Separate table linked to product — keeps product table clean
when most items are not consignment. Tracks consignor (account),
commission percentage, min price, and agreement date.
33 tests passing.

packages/backend/src/db/migrations/meta/_journal.json

@@ -43,6 +43,13 @@
       "when": 1774653515690,
       "tag": "0005_add_products_units_receipts",
       "breakpoints": true
+    },
+    {
+      "idx": 6,
+      "version": "7",
+      "when": 1774653924179,
+      "tag": "0006_add_consignment",
+      "breakpoints": true
     }
   ]
 }