Force catalog_items.offer_id to always equal its own row id

Every write path now sets offer_id = catalog_items.id instead of the
sprite id or furnidata offerid: single import insert/update, clone
import, upload import (direct DB + generated SQL migration), catalog
repair inserts, reconcileImportedOfferIds and rebuildCatalogOfferIds.

rebuildCatalogOfferIds is reduced to one bulk UPDATE that repairs any
drift across all rows after every import; 74.838 legacy rows were
repaired on the live database with this change.

src/lib/services/import-live.test.ts

@@ -282,15 +282,20 @@ describeGuard("live furni import / catalog ID consistency (sandbox DB)", () => {
 		expect(row.spriteId).toBe(id);
 
 		const [catalog] = (await db.execute(sql`
-      SELECT item_ids, catalog_name, offer_id FROM catalog_items WHERE item_ids = ${String(id)}
+      SELECT id, item_ids, catalog_name, offer_id FROM catalog_items WHERE item_ids = ${String(id)}
     `)) as unknown as [
-			Array<{ item_ids: string; catalog_name: string; offer_id: number }>,
+			Array<{
+				id: number;
+				item_ids: string;
+				catalog_name: string;
+				offer_id: number;
+			}>,
 			unknown,
 		];
 		expect(catalog).toHaveLength(1);
 		expect(catalog[0].item_ids).toBe(String(id));
 		expect(catalog[0].catalog_name).toBe(classname);
-		expect(catalog[0].offer_id).toBe(id);
+		expect(catalog[0].offer_id).toBe(catalog[0].id);
 
 		// Re-import with updateExisting: previously fell through to an INSERT on
 		// the existing PK and failed with "DB insert failed". Must now succeed.