Use floating numbers for OSD frame position

If there are multiple monitors with different resolutions, integer
values may cause placing the OSD outside of the visible area.
Floating values are relative to the current monitor size and OSD
is always placed inside the visible area.

pw-ui.el

@@ -60,8 +60,8 @@ The indicator is displayed only on graphical terminals."
   :group 'pipewire)
 
 (defcustom pipewire-osd-frame-parameters
-  `((left . (+ 50))
-    (top . (- 50)))
+  `((left . 0.05)
+    (top . 0.95))
   "Alist of frame parameters for the on screen display indicator."
   :type '(alist :key-type symbol :value-type sexp)
   :group 'pip-frame)
@@ -193,6 +193,7 @@ The indicator is displayed only on graphical terminals."
         (setq pw-ui--osd-frame (make-frame `((unsplittable . t)
                                              ,@pipewire-osd-frame-parameters
                                              (minibuffer . nil)
+                                             (parent-frame . ,(selected-frame))
                                              (width . ,(+ 2 (length string)))
                                              (height . 1)
                                              (min-width . 1)