fix(lint): exempt next-env.d.ts triple-slash + declare globalEnv vars

next-env.d.ts is a generated file using triple-slash references that
TypeScript requires. ESLint exemption added in apps/web-next config only.
Also declare CI, DATABASE_URL, PAYLOAD_SECRET, NODE_ENV in turbo.json
globalEnv so turbo/no-undeclared-env-vars stops warning.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

turbo.json

@@ -1,5 +1,6 @@
 {
   "$schema": "https://turborepo.dev/schema.json",
+  "globalEnv": ["CI", "DATABASE_URL", "PAYLOAD_SECRET", "NODE_ENV"],
   "tasks": {
     "build": {
       "dependsOn": ["^build"],