feat: auto-create avatars storage bucket on server startup

Uses Next.js instrumentation.ts to ensure the Supabase "avatars"
bucket exists on first boot — no manual setup needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/editor/instrumentation.ts

@@ -0,0 +1,24 @@
+export async function register() {
+  // Only run on the server
+  if (process.env.NEXT_RUNTIME === 'nodejs') {
+    const { createClient } = await import('@supabase/supabase-js')
+
+    const url = process.env.NEXT_PUBLIC_SUPABASE_URL
+    const key = process.env.SUPABASE_SERVICE_ROLE_KEY
+    if (!url || !key) return
+
+    const supabase = createClient(url, key)
+
+    const { data: buckets } = await supabase.storage.listBuckets()
+    const exists = buckets?.some((b) => b.name === 'avatars')
+
+    if (!exists) {
+      await supabase.storage.createBucket('avatars', {
+        public: true,
+        fileSizeLimit: 5 * 1024 * 1024, // 5MB
+        allowedMimeTypes: ['image/png', 'image/jpeg', 'image/webp', 'image/gif'],
+      })
+      console.log('Created "avatars" storage bucket')
+    }
+  }
+}