docs(hardware): put the patch panel back above the PDU

[Gerrrt]

What changed

Two rows in the Rack table in docs/hardware.md. U7 is the PDU and U8 is the patch panel; they were listed the other way round. A short note under the table records the correction, following the oracle entry in Compute.

Nothing about the running lab changes — this is documentation matching the rack.

Why

Closes #162. Confirmed against the rack on 2026-08-29, after this table and the wiki's rack page were found to disagree about exactly these two slots and neither could settle it on paper.

Everything else in the table is right, which is what makes this two swapped rows rather than a numbering-direction problem: U1–U2 holds the UPS at the bottom and U9 the switch at the top, so higher U means higher in the rack, and every other row matches what is bolted in.

The note is deliberate rather than a silent swap. The two documents disagreed and this one lost; leaving no trace of that invites whoever reconciles them next to swap it back.

Blast radius

None. Nothing in this repository reads the rack order — check_docs.py cross-checks the Compute table against docs/network.md and never looks at the Rack table, and no diagram, runbook or config references the U position of either device.

Worth stating plainly that nothing was ever at risk outside the repo either. The rack order is load-bearing for the household's printed emergency card, which says to unplug "the box at the very top" and power-cycle "the 5th box from the top" — the switch and morpheus. Neither moves. The swap is between the second and third units, below the top slot and above the fifth, so the count to morpheus is unchanged under either version. Wrong documentation, not a wrong instruction.

• No change to network segmentation or firewall rules
• No new port published to a VLAN that could not already reach the service
• No credential added outside secrets/*.sops.yaml

Verification

Ran both CI checks locally against the change:

$ python3 scripts/check_docs.py
docs OK — 35 Prometheus + 13 Loki rules, 5 dashboards, 84 panels, 6 assertions

$ npx markdownlint-cli2
Summary: 0 issues in 0 files   (34 files linted)

• make validate passes — check_docs.py and markdownlint-cli2 as above; this change touches no compose or secrets input
• Deployed to the lab and confirmed working — n/a, documentation only
• Docs updated (docs/, service README, or docs/roadmap.md)

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Built in a scratch worktree off origin/main, because the checkout on this machine is mid-change on claude/ups-battery-proven-4299dc with uncommitted work in stacks/observability/compose.yaml. That branch and its working tree were left untouched.