feat(power): clamshell — ignore lid suspend when docked (#86)

Explicit HandleLidSwitchDocked=ignore under services.logind so closing
the lid with an external display connected does not suspend. Undocked
lid path left to upstream defaults. checks.clamshell-logind asserts the
baked logind.conf and active logind; real multi-monitor lid V3 queued.

Verified: V2 — flake check --no-build; checks.clamshell-logind green.
V3 pending: HARDWARE-QUEUE #86 lid+external on a laptop.

agent/BACKLOG.md

@@ -55,13 +55,6 @@ runtime-computed `resume_offset` into the boot cmdline, and the dev box runs
 exactly this layout (`/proc/cmdline` verified) but isn't Nomarchy. Steps in
 HARDWARE-QUEUE. Close #76 on PASS.
 
-### 86. Clamshell dock: lid + external monitor (`VISION § C`)
-Lid closed with external monitor connected must not suspend
-(`logind` `lidSwitchDocked` / `ExternalPower` audit + display-profile
-interplay); wake behaves. Display profiles + auto-switch already exist —
-this is the lid/suspend edge case. VM where possible; residual V3 on
-real dock hardware.
-
 ### 87. Dock audio sink follows plug/unplug (`VISION § C`)
 Default audio sink: dock sink on plug, internal on unplug (WirePlumber
 policy or udev hook). Complements #86; can ship independently.
@@ -118,8 +111,8 @@ high-ROI, etc.) live in the journal + ROADMAP — not here.*
   2026-07-10). Keep #59 commented install guidance; no
   `nomarchy.hardware.nvidia.*` until a hybrid maintainer + queue.
 
-_(#80–#83 + #85 shipped 2026-07-11. #84 split → **NEXT #86–#87** dock
-  clamshell + dock audio.)_
+_(#80–#83 + #85–#86 shipped 2026-07-11. Remaining dock slice: **#87**
+  dock audio. #86 V3 clamshell on real external display → HARDWARE-QUEUE.)_
 
 ### v1.0 pointer