feat(01-01): configure environment variables for Supabase

- .env.example template for required variables
- .env.local with placeholders (gitignored)
- NEXT_PUBLIC_SUPABASE_URL for API endpoint
- NEXT_PUBLIC_SUPABASE_ANON_KEY for client-side auth
- SUPABASE_SERVICE_ROLE_KEY for server-side operations
- NEXT_PUBLIC_APP_URL for callback URLs

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

.env.example

@@ -0,0 +1,7 @@
+# Supabase Configuration
+NEXT_PUBLIC_SUPABASE_URL=your-project-url
+NEXT_PUBLIC_SUPABASE_ANON_KEY=your-anon-key
+SUPABASE_SERVICE_ROLE_KEY=your-service-role-key
+
+# App Configuration
+NEXT_PUBLIC_APP_URL=http://localhost:3000