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.

modules/home/idle.nix

@@ -85,8 +85,9 @@ in
           # Suspend only on battery, and sooner than the old fixed 30 min
           # (it now only fires unplugged). Plugged in, the machine stays
           # up — long builds, media, presentations aren't killed mid-idle.
-          # Closing the lid still suspends on AC (logind's default): that's
-          # an explicit "I'm done", distinct from sitting idle.
+          # Lid close is logind's job (not hypridle): undocked lid still
+          # suspends (HandleLidSwitch); docked/clamshell lid is ignore
+          # (HandleLidSwitchDocked — modules/nixos/power.nix, #86).
           { timeout = 900; on-timeout = "${onAc} || systemctl suspend"; }
         ];
       };