chore(turbo): declare USE_DEV_SEED in globalEnv

Earlier commit 74b88f7 attempted this but the Edit failed silently
without a prior Read. ESLint's turbo/no-undeclared-env-vars rule was
still flagging the warning.

turbo.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://turborepo.dev/schema.json",
-  "globalEnv": ["CI", "DATABASE_URL", "PAYLOAD_SECRET", "NODE_ENV"],
+  "globalEnv": ["CI", "DATABASE_URL", "PAYLOAD_SECRET", "NODE_ENV", "USE_DEV_SEED"],
   "boundaries": {
     "tags": {
       "app": {