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.

docs/ROADMAP.md

@@ -389,6 +389,11 @@ Design/decision records and a running log of shipped work (items marked
   ✓ **Hardware hall of fame (#85, `VISION § F`):** HARDWARE.md §9
   install-tested table (T14s Gen 4, Latitude 5410/5310) + “send your DMI
   line” PR invite; §10 points contributors at the table.
+  ✓ **Clamshell logind (#86, `VISION § C`):** explicit
+  `services.logind.settings.Login.HandleLidSwitchDocked = "ignore"` when
+  power management is on (systemd docked = external display present).
+  Undocked lid suspend left to upstream. `checks.clamshell-logind` asserts
+  logind.conf + active logind. Real lid+external V3 in HARDWARE-QUEUE.
 - ✓ **Hibernate double-unlock:** on resume from hibernate the LUKS
   passphrase already gates the machine, but locking hyprlock before sleep
   meant a second password. Fixed by *not locking* before an encrypted