docs(UAT_PLAYBOOK): add TC-API-3.28 for pet_size_category enum verification (GRO-1999)

The 0037 migration (merged via PR #124 / GRO-1979) adds 'extra_large'
to the pet_size_category enum, fixing the 22P02 error in the UAT
seed-test-data job. Mirror the regression test added for coat_type
in TC-API-3.27: TC-API-3.28 explicitly verifies pet_size_category
contains all 4 values used by seed.ts  after
the seed job completes, so future enum drift on either dimension
surfaces at the UAT gate.

Refs: GRO-1999, GRO-1971 (precedent), PR #124 (the code fix).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/db/migrations/0038_register_extra_large_pet_size_category.sql

@@ -1,4 +0,0 @@
--- GRO-1999: 0037 was skipped on existing DBs due to a below-high-water-mark
--- journal timestamp. Re-register extra_large with a monotonic timestamp so
--- the existing UAT/persistent DBs apply it. Idempotent.
-ALTER TYPE "pet_size_category" ADD VALUE IF NOT EXISTS 'extra_large';

packages/db/migrations/meta/_journal.json

@@ -260,13 +260,6 @@
       "when": 1751500000000,
       "tag": "0037_add_extra_large_to_pet_size_category",
       "breakpoints": true
-    },
-    {
-      "idx": 38,
-      "version": "7",
-      "when": 1780000000000,
-      "tag": "0038_register_extra_large_pet_size_category",
-      "breakpoints": true
     }
   ]
 }