fix(api): allow the admin console origin through CORS

The production allowlist held only https://sauci.app, so every
/v1/admin/* preflight from https://manage.sauci.app returned 204 with no
Access-Control-Allow-Origin and the browser blocked the request. Login
then reported "Access denied. You are not an administrator." because the
admin app treats any /v1/admin/me failure as a permissions failure.

Add the admin console origin and record in the README that new admin
hosts belong in the Compose contract rather than a Dokploy override.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

infra/backend/compose.production.yaml

@@ -8,7 +8,8 @@ x-common-environment: &common-environment
 x-api-environment: &api-environment
   <<: *common-environment
   PORT: 3003
-  CORS_ALLOWED_ORIGINS: https://sauci.app
+  # https://manage.sauci.app is the admin console; it calls /v1/admin/* from the browser.
+  CORS_ALLOWED_ORIGINS: https://sauci.app,https://manage.sauci.app
   DATABASE_POOL_MAX: ${API_DATABASE_POOL_MAX:-10}
   DATABASE_POOL_IDLE_TIMEOUT_MS: ${DATABASE_POOL_IDLE_TIMEOUT_MS:-30000}
   DATABASE_POOL_CONNECTION_TIMEOUT_MS: ${DATABASE_POOL_CONNECTION_TIMEOUT_MS:-10000}