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/jupiter/configuration.nix

@@ -13,6 +13,7 @@
     ../../services/containers.nix
     ../../services/network/caddy.nix
     ../../services/vpn/tailscale.nix
+    ../../services/monitoring/node-exporter.nix
     ../../services/media/jellyfin.nix
     ../../services/media/sabnzbd.nix
     ../../services/media/prowlarr.nix

hosts/mars/configuration.nix

@@ -11,6 +11,7 @@
     ../../common.nix              # shared base: user / ssh / nix / firewall
     ../../services/containers.nix
     ../../services/vpn/tailscale.nix
+    ../../services/monitoring/node-exporter.nix
   ];
 
   networking.hostName = "mars";

hosts/mercury/configuration.nix

@@ -10,6 +10,7 @@
     ../../services/network/unbound.nix      # local recursive resolver (127.0.0.1:5335)
     ../../services/network/pihole.nix        # DNS adblock + DHCP (declarative static leases)
     ../../services/vpn/tailscale.nix        # tailnet node (headscale on neptun)
+    ../../services/monitoring/node-exporter.nix
   ];
 
   networking.hostName = "mercury";

hosts/neptun/configuration.nix

@@ -9,6 +9,7 @@
     ../../common.nix              # shared base: user / ssh / nix / firewall
     ../../services/network/caddy.nix
     ../../services/vpn/tailscale.nix
+    ../../services/monitoring/node-exporter.nix
     ../../services/identity/authentik.nix
     ../../services/vpn/headscale.nix
     ../../services/vpn/headplane.nix

hosts/terra/configuration.nix

@@ -15,6 +15,7 @@ in
     ../../common.nix
     ../../services/containers.nix
     ../../services/vpn/tailscale.nix
+    ../../services/monitoring/node-exporter.nix
     ../../services/desktop/desktop-hyprland.nix
     ../../services/desktop/desktop-apps.nix
     ../../services/desktop/librechat.nix

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"))