feat(nixos): add multi-arch support and refactor system configs

- add aarch64-linux to supported systems (flake + pkgs)
- refactor host definitions into tty/desktop/laptop configurations
- introduce sharedModules to reduce duplication
- split system modules into base, gui, and laptop groups
- add headless (tty) configuration

feat(fish): add Ctrl+Delete and Alt+Delete bindings
- Ctrl+Delete → kill-word
- Alt+Delete → kill-token

chore(hosts): remove explicit hostname from aesthetic

chore(services): remove forced disable of speechd

system/services/default.nix

@@ -11,7 +11,6 @@
 
     irqbalance.enable = true;
     thermald.enable = true;
-    speechd.enable = lib.mkForce false;
   };
 
   # Use in place of hypridle's before_sleep_cmd, since systemd does not wait for