fix(web): add API_URL to turbo.json globalEnv

Turborepo was not passing the API_URL environment variable to the build
process, causing Next.js rewrites to fall back to the default test API
instead of the production API configured in Vercel.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

turbo.json

@@ -1,6 +1,7 @@
 {
   "$schema": "https://turbo.build/schema.json",
   "globalDependencies": ["tsconfig.json", "tsconfig.base.json"],
+  "globalEnv": ["API_URL"],
   "tasks": {
     "build": {
       "dependsOn": ["^build"],