Fix cold-start docs link to use relative .mdx path

The unreleased deployment-cold-start page only lives in docs/docs/, not in
the versioned snapshots. Slug-based links like /deployment-cold-start resolve
to the latest released version (1.9.0) and break the docusaurus build.
Relative .mdx links resolve within the same docs version.

Author: ogabrielluiz

docs/docs/Deployment/deployment-docker.mdx

@@ -279,4 +279,4 @@ For a minimal Dockerfile that adds `uv` to the 1.8.0 image, see the [release not
 
 ## Cold-start optimization
 
-For guidance on reducing cold-start time in containerized deployments (scale-from-zero, serverless, pre-baked images), see [Cold-start optimization](/deployment-cold-start).
+For guidance on reducing cold-start time in containerized deployments (scale-from-zero, serverless, pre-baked images), see [Cold-start optimization](./deployment-cold-start.mdx).

docs/docs/Deployment/deployment-prod-best-practices.mdx

@@ -125,4 +125,4 @@ Follow industry best practices and use secure Langflow configurations, such as t
 * [Deploy the Langflow production environment on Kubernetes](/deployment-kubernetes-prod)
 * [Langflow Helm Charts repository](https://github.com/langflow-ai/langflow-helm-charts)
 * [Langflow environment variables](/environment-variables)
-* [Cold-start optimization](/deployment-cold-start)
+* [Cold-start optimization](./deployment-cold-start.mdx)