feat(flake): register lyrathorpe-rpi5 host

Add the aarch64-linux Raspberry Pi 5 host to the host table: the RPi5
machine config, the raspberry-pi-5 nixos-hardware profile, and key-only
sshd. Headless, so no swaywm.nix; base home modules only.

flake.nix

@@ -288,6 +288,22 @@
               ./lyrathorpe/home/work.nix
             ];
           };
+
+          lyrathorpe-rpi5 = {
+            system = "aarch64-linux";
+            username = "lyrathorpe";
+            fullName = "Lyra Thorpe";
+            portable = false;
+            # Headless server: Docker host + nginx reverse proxy. No swaywm.nix
+            # (no desktop); the raspberry-pi-5 profile supplies kernel/firmware,
+            # ssh.nix adds key-only sshd.
+            modules = [
+              ./system/machine/RPi5/configuration.nix
+              inputs.nixos-hardware.nixosModules.raspberry-pi-5
+              ./system/modules/ssh.nix
+            ];
+            homeModules = [ ./lyrathorpe/home ];
+          };
         };
 
         # Darwin host table — macOS machines built via mkDarwinHost. The shared