docs(site-explorer): document the mlx-devices firmware report

[chet]

site-explorer mlx-devices reports each BlueField/Mellanox card's part number, NIC firmware version, and serial straight from explored Redfish PCIe inventory -- the only way to spot a NIC-mode DPU on outdated firmware, since a card in NIC mode can't report its own. Nothing in docs/ mentions it.

What this involves

• A section under Operations -> DPU Management (likely in dpu-management/dpu-lifecycle-management.md's firmware coverage, or a short page beside it): what the report shows, the NIC-mode motivation, and that the data is the host BMC's view -- no new collection.
• Regenerate the admin-cli docs corpus scoped to the site-explorer group so the command gets its generated page -- the corpus predates the command and nothing gates it in CI.
• The CLI flags and output stayed stable across the RPC pagination rework (refactor(site-explorer): paginate the explored Mellanox device RPC #2833), so one pass covers both PRs.

Satisfies the v2.0 checklist rows for #2757 and #2833.

Part of #3640.