feat(dnd): swaync Do-Not-Disturb toggle + Waybar bell indicator

Adds a Do-Not-Disturb story on top of swaync:

- Waybar `custom/notification` module via `swaync-client -swb` — streams
  the notification count + DND state (no polling). Left-click toggles the
  panel, right-click toggles DND; bell-off glyph + muted color when DND is
  on, accent when notifications are waiting.
- `nomarchy-menu dnd` toggle in the root picker and bound to SUPER+CTRL+D
  (so it shows in the SUPER+? cheatsheet). Turning DND off confirms with a
  toast; turning it on is silent — notifications are suppressed and the
  bell-off icon is the cue.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/keybinds.nix

@@ -47,6 +47,7 @@
     { mods = "$mod CTRL";   key = "B";      action = "exec, nomarchy-menu bluetooth"; desc = "Bluetooth"; }
     { mods = "$mod CTRL";   key = "S";      action = "exec, nomarchy-menu capture";   desc = "Screenshot / capture"; }
     { mods = "$mod CTRL";   key = "A";      action = "exec, nomarchy-menu ask";       desc = "Ask Claude"; }
+    { mods = "$mod CTRL";   key = "D";      action = "exec, nomarchy-menu dnd";       desc = "Do Not Disturb toggle"; }
 
     # Focus
     { mods = "$mod";        key = "H";      action = "movefocus, l";                  desc = "Focus left"; }