feat(nixos): physical-host services — power, bluetooth, OOM, firmware

- thermald on the x86 hosts (guarded; the Asahi MBP self-governs).
- T400 battery charge thresholds (75/80) via tp_smapi; tlp itself comes
  from the nixos-hardware profile.
- Bluetooth (bluez + powerOnBoot) and blueman on the laptops — the MBP
  already loads Apple BT firmware but bluez was never running.
- earlyoom + fwupd on the physical graphical hosts; zram on the Mac Pro.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

system/modules/laptop.nix

@@ -12,4 +12,13 @@
     enable = true;
     settings.General.EnableNetworkConfiguration = true;
   };
+
+  # Bluetooth. The Asahi MBP loads Apple's BT firmware (see its host config) and
+  # the T400 has an optional BT module; enable bluez on both, with blueman as the
+  # GUI/tray manager for the Sway session.
+  hardware.bluetooth = {
+    enable = true;
+    powerOnBoot = true;
+  };
+  services.blueman.enable = true;
 }