perf(ui): the dialogs you type in no longer sit on a blurred backdrop

A backdrop-filter covers the whole window and is recomputed every time
anything above it repaints. Behind these dialogs is an application that
never stops moving — CAT polls four times a second, spots arrive, meters
sweep, maps redraw — so the filter was being recomputed continuously, and
each keystroke's repaint dragged a full-window blur with it. That is why
the lag was felt in Preferences and nowhere else, and why fixing the
cluster macros did not end it.

Worse in one place: the cluster server editor opens FROM Preferences, so
its overlay was the SECOND full-window filter stacked over the first.
That is exactly where the delay was first reported.

The dialogs an operator types in for minutes — Preferences, the cluster
editor, the QSO editor, bulk edit, alert rules, award definitions — now
dim the background harder instead of blurring it. Everything else keeps
the blur: a confirmation you click through in a second costs nothing.

frontend/src/components/BulkEditModal.tsx

@@ -193,7 +193,7 @@ export function BulkEditModal({ open, ids, onClose, onApplied }: Props) {
 
   return (
     <Dialog open={open} onOpenChange={(o) => { if (!o) onClose(); }}>
-      <DialogContent className="max-w-md">
+      <DialogContent overlayBlur={false} className="max-w-md">
         <DialogHeader>
           <DialogTitle>{t('bulk.title')}</DialogTitle>
           <DialogDescription>