Run notification click actions as safe argv (backport of #7926)

Backport of the notification click-command hardening (PR #7926, merged to
quattro as 43bfe9b9) onto the v4-0-1 release branch. Click actions are argv
vectors run without a shell, omarchy-notification-send calls the Notify D-Bus
method directly via busctl instead of notify-send, and --exec takes the command
as rest-of-line words. Excludes docs/notifications.md, which does not exist on
v4-0-1.

default/hypr/helpers.lua

@@ -136,7 +136,7 @@ function o.bind_toggle(keys, description, toggle, options)
 end
 
 function o.notify(message)
-  return "notify-send -u low " .. shell_quote(message)
+  return "omarchy-notification-send -u low " .. shell_quote(message)
 end
 
 function o.window(match, rules)