add node_exporter host vitals + quickshell HUD

Prometheus node_exporter enabled on every host, plus a quickshell widget
(SUPER+CTRL+V on terra) to view live CPU/mem/disk/net/uptime without a
separate dashboard.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011FHr5ug9pu8q4XPrRkFnzJ

hosts/terra/home/hyprland.nix

@@ -204,6 +204,8 @@ in
         (bind "SUPER + CTRL + 0" (dsp.exec "qs kill; sleep 0.3; qs"))
         # toggle the Slant sidebar
         (bind "SUPER + CTRL + S" (dsp.global "quickshell:sidebar"))
+        # toggle the host vitals HUD
+        (bind "SUPER + CTRL + V" (dsp.global "quickshell:vitals"))
 
         (bind "SUPER + B" (dsp.exec "vivaldi"))
         (bind "SUPER + E" (dsp.exec "cosmic-files"))