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/shipping/fedex-rates.ts

@@ -11,12 +11,12 @@
  *
  * TODO(migration): shipping is dormant in the SaaS rebuild. The
  * legacy `shipping_settings` table (with the FedEx credential columns
- * this file needs) is still present in the database — see
- * supabase/migrations/083_shipping_settings.sql — but the new
- * `db/schema/` does not declare it. The data reads below hit the
- * legacy table directly via `pool.query`. When shipping comes back,
- * declare the table in `db/schema/shipping.ts` and switch the reads
- * to Drizzle.
+ * this file needs) is still present in the database — originally from
+ * the now-archived supabase migrations, consolidated into
+ * `db/migrations/0001_init.sql` — but the new `db/schema/` does not
+ * declare it. The data reads below hit the legacy table directly via
+ * `pool.query`. When shipping comes back, declare the table in
+ * `db/schema/shipping.ts` and switch the reads to Drizzle.
  */
 
 import { getAdminUser } from "@/lib/admin-permissions";