chore(comments): re-point dangling supabase/migrations breadcrumbs

The Supabase purge deleted the archived supabase/migrations/.archived/
directory, but 12 src/ files still referenced its files by path in
JSDoc / TODO comments. The references were misleading (pointing to
deleted files), so re-point them at the canonical location of those
RPCs in db/migrations/0001_init.sql. No code or behavior changes.

Also fixed a stray 'supabase shim returns empty results' comment in
src/app/admin/page.tsx (the shim was already removed in Step 3 of
the refactor).

src/actions/import-orders.ts

@@ -11,8 +11,9 @@ export type ImportOrdersResult =
 
 /**
  * Bulk-import orders. Replaces the legacy `create_order_with_items` SECURITY
- * DEFINER RPC (`supabase/migrations/021_shipping_only_brand.sql`). The new
- * `orders` schema doesn't have `subtotal`, `customer_name`, `customer_email`,
+ * DEFINER RPC (originally from the now-archived supabase migrations;
+ * consolidated into `db/migrations/0001_init.sql`). The new `orders`
+ * schema doesn't have `subtotal`, `customer_name`, `customer_email`,
  * `customer_phone`, or `stop_id` columns — totals are stored in
  * `total_cents` and customers are referenced by `customer_id`. For each
  * imported order we upsert a `customers` row keyed on email+tenant, then