Add display identification overlays

config/dot/quickshell/shell.qml

@@ -86,6 +86,8 @@ ShellRoot {
         Osd {}
     }
 
+    DisplayIdentify {}
+
     // ── Single-instance overlays ────────────────────────────────────────────
     // These are always constructed but only *visible* when ShellState says so.
     // They're cheap while hidden, and keeping them alive means opening the