Send notifications via the Notify D-Bus method, never notify-send

omarchy-notification-send now calls org.freedesktop.Notifications.Notify
directly with `busctl --user`, instead of shelling out to notify-send. Each
value is one typed D-Bus parameter, so there is no argv/option layer that could
reinterpret a relayed headline like `--hint=…` or `-rf` as an option or a hint:
the summary and body are strings, and omarchy-exec-argv is built only from
--exec. A leading `--` keeps busctl's own getopt from reading a dash-leading
value as a busctl option.

Map -i to app_icon, -t to expire_timeout, and urgency to the byte hint; unknown
options are now a hard error rather than a silent pass-through. Route the unused
hypr o.notify helper and the sample hooks through the wrapper too, and tighten
the bin-style test so nothing under bin/ may call notify-send. The test stubs
busctl and trips if notify-send is invoked.

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)