feat(power): suspend-then-hibernate 1h on battery (#115)

Human decision: 1h delay, battery only, Preferences enable/disable.
Wire systemd suspend-then-hibernate + HibernateDelaySec=1h +
HibernateOnACPower=false when settings.power.suspendThenHibernate is on
and boot.resumeDevice is set. Lid: s2h undocked, plain suspend on AC.
nomarchy-suspend for hypridle + Power menu (live state). LUKS unlock
before encrypted hibernate so s2h→disk is not double-password.
state-bridges assert the policy; HARDWARE-QUEUE #115 + suggested order.

V1: nix flake check --no-build. V3: bag-carry on hardware.

modules/nixos/options.nix

@@ -143,6 +143,26 @@
           Needs nomarchy.system.power.laptop.
         '';
       };
+
+      # #115: suspend → hibernate after 1h on battery. Default true so a
+      # bag-carried laptop stops draining without a menu trip; Preferences
+      # flips settings.power.suspendThenHibernate (state bridge). No-op
+      # when boot.resumeDevice is unset (no hibernate path).
+      suspendThenHibernate = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        defaultText = lib.literalExpression
+          "(settings.power.suspendThenHibernate from state.json) or true";
+        description = ''
+          When true and hibernation is wired (boot.resumeDevice), idle and
+          undocked lid-close use systemd suspend-then-hibernate on battery:
+          sleep, then hibernate after HibernateDelaySec (1 hour). On AC,
+          plain suspend only (HibernateOnACPower=false; lid uses
+          HandleLidSwitchExternalPower=suspend). Toggle from System ›
+          Preferences › Suspend then hibernate — needs a system rebuild for
+          logind; nomarchy-suspend reads the live state for menu/hypridle.
+        '';
+      };
     };
   };
 }