Docs: update replication docs

[Blargian]

Summary

Updates the following replication docs to be easier to follow:

• https://clickhouse.com/docs/architecture/horizontal-scaling
• https://clickhouse.com/docs/architecture/replication
• https://clickhouse.com/docs/architecture/cluster-deployment

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/integrations/index.mdx

[vercel]

@Blargian is attempting to deploy a commit to the ClickHouse Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
clickhouse-docs	✅ Ready (Inspect)	Visit Preview		Jun 30, 2025 0:53am
clickhouse-docs-ru	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 30, 2025 0:53am
clickhouse-docs-zh	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 30, 2025 0:53am