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/machine/MacPro31/configuration.nix

@@ -22,6 +22,10 @@
 
   networking.hostName = "MacPro31-NixOS";
 
+  # Elderly host: a compressed RAM swap softens memory pressure (earlyoom in
+  # workstation.nix is the backstop).
+  zramSwap.enable = true;
+
   # This host accepts SSH, so open 22 (the firewall itself is enabled in
   # workstation.nix with a default-deny policy).
   services.openssh.enable = true;

system/machine/T400/configuration.nix

@@ -1,7 +1,7 @@
 # ThinkPad T400 (NixOS). Shared laptop options live in ../../modules/laptop.nix;
 # only host-specific settings are here. Install notes (boot variants, GPU,
 # partitions): see ./README.md.
-{ ... }:
+{ config, ... }:
 
 {
   imports = [
@@ -31,6 +31,16 @@
   # the radeon firmware needed by the discrete GPU below.
   hardware.cpu.intel.updateMicrocode = true;
 
+  # Battery longevity: cap charging to 75-80%. tlp itself comes from the
+  # nixos-hardware lenovo-thinkpad profile; tp_smapi supplies the threshold
+  # sysfs on this 2008-era ThinkPad (kernel-native natacpi is too new for it).
+  boot.kernelModules = [ "tp_smapi" ];
+  boot.extraModulePackages = [ config.boot.kernelPackages.tp_smapi ];
+  services.tlp.settings = {
+    START_CHARGE_THRESH_BAT0 = 75;
+    STOP_CHARGE_THRESH_BAT0 = 80;
+  };
+
   # This T400 has the optional discrete GPU fitted: an ATI Mobility Radeon HD
   # 3470 (RV620), driven by the open `radeon` KMS driver. Load it in the initrd
   # for early modesetting (clean Sway/Wayland start); firmware comes from