[v25.2.x] cluster/health: use kafka high watermark in partition_status

Backport https://github.com/redpanda-data/redpanda/pull/30873 to branch v25.2.x. This issue was created as a placeholder because the original PR's commit(s) could not be automatically cherry-picked. Here are the commands to execute: ``` git checkout v25.2.x git checkout -b manual-backport-30873-v25.2.x-252 git cherry-pick -x f4352ada31 git push origin manual-backport-30873-v25.2.x-252 gh pr create \ --title "[v25.2.x] cluster/health: use kafka high watermark in partition_status" \ --base "v25.2.x" \ --label "kind/backport" \ --head "manual-backport-30873-v25.2.x-252" \ --draft \ --repo "redpanda-data/redpanda" \ --milestone "v25.2.x-next" \ --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/30873 "