docs: remove the deploy lifecycle page after the topic split

What

docs/docs/how-tos/deploy.mdx has been split into one page per topic:

• Prepare to deploy (prepare-to-deploy.mdx)
• Deploy a cluster (deploy-cluster.mdx)
• Cloudflare DNS (cloudflare-dns.mdx)
• Keycloak authentication (keycloak-auth.mdx)
• Update a cluster (update-cluster.mdx)
• Destroy a cluster (destroy-cluster.mdx)

After those merge, deploy.mdx is only pointer sections. This issue removes the page and repoints the remaining links.

Why

The page no longer carries its own content. Keeping it adds an extra hop (provider page to deploy.mdx to the topic page) and a second place to maintain. Removing it matches the original "split into one page per topic" intent.

Scope

Repoint remaining links to deploy.mdx

After the split PRs (#654, #656, and the deploy/destroy splits) merge, these still target deploy.mdx:

• aws.mdx: deploy#what-every-deployment-includes
• hetzner.mdx: deploy#what-every-deployment-includes, deploy#deploy-and-verify (twice), deploy#destroy

Repoint them: #deploy-and-verify to /docs/how-tos/deploy-cluster and #destroy to /docs/how-tos/destroy-cluster.

For #what-every-deployment-includes, drop the link (the ## What every deployment includes section is being removed, not relocated); reword the provider sentence.

Remove the page

• Delete docs/docs/how-tos/deploy.mdx.
• Remove how-tos/deploy from docs/sidebars.js.

Acceptance criteria

• deploy.mdx is removed and no longer in the sidebar
• No internal links point to /docs/how-tos/deploy or its anchors
• Docusaurus build passes with no broken links or anchors

Dependencies

Do this after the split PRs merge (#654, #656, and the deploy/destroy/update splits) so the link repointing is done against the final state rather than conflicting with the open PRs.

Part of #630.