Refresh bar widgets on every monitor, not just one

A bar surface is built per monitor, so a widget in the layout is live once
per screen — but an IPC target only ever routes to the handler that
registered first. `omarchy.indicators refresh` therefore reached a single
bar, and since indicators only re-read their state on that signal, the
other screens kept showing a stale reminder count, tmux alert, or DND
state until the next reload. Clock and system-update refreshes had the
same reach.

Let the bar resolve every live instance of a widget id and relay the call
to all of them.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

shell/plugins/bar/widgets/SystemUpdate.qml

@@ -28,11 +28,11 @@ BarWidget {
     target: "omarchy.system-update"
 
     function refresh(): void {
-      root.refresh()
+      root.broadcast("refresh")
     }
 
     function clear(): void {
-      root.clear()
+      root.broadcast("clear")
     }
   }