fix: skip env validation during Docker builds with placeholder vars

The ensureInitialized() env check threw on missing SUPABASE_SERVICE_ROLE_KEY
and CRON_SECRET during Next.js page collection at Docker build time. These
server-only vars are injected at runtime, not build time.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/init.ts

@@ -30,6 +30,13 @@ const OPTIONAL_VARS = [
 ] as const
 
 function validateEnvironment(): void {
+  // During Docker builds, NEXT_PUBLIC_* vars are placeholder sentinels
+  // replaced at runtime by docker-entrypoint.sh. Server-only vars like
+  // SUPABASE_SERVICE_ROLE_KEY are not available at build time at all.
+  // Skip validation so Next.js page collection doesn't fail.
+  const isBuildPlaceholder = process.env.NEXT_PUBLIC_SUPABASE_URL?.startsWith('__')
+  if (isBuildPlaceholder) return
+
   const missing: string[] = []
 
   for (const v of REQUIRED_CORE_VARS) {