perf: replace window.confirm() with Dialog components

[macwilling]

Problem

Three places use window.confirm() — a synchronous browser API that blocks the entire JavaScript event loop, causing long tasks and poor INP scores. Chrome on Android may silently suppress it entirely.

File	Issue
components/clients/ArchiveClientButton.tsx:19	window.confirm() before archive
components/tasks/AttachmentsList.tsx:139	window.confirm() before delete attachment
components/comments/CommentThread.tsx:54	window.confirm() before delete comment

Fix

Replace each window.confirm() with a controlled <Dialog> — the same pattern already used in DeleteTaskButton. Each trigger button opens the dialog instantly (zero latency), and the destructive action lives in the dialog footer.

// Pattern (ArchiveClientButton example)
const [confirmOpen, setConfirmOpen] = useState(false);

<Button onClick={() => setConfirmOpen(true)}>Archive</Button>

<Dialog open={confirmOpen} onOpenChange={setConfirmOpen}>
  <DialogContent>
    <DialogHeader>
      <DialogTitle>Archive this client?</DialogTitle>
      <DialogDescription>They will be hidden from the active client list.</DialogDescription>
    </DialogHeader>
    <DialogFooter>
      <DialogClose asChild><Button variant="outline">Cancel</Button></DialogClose>
      <Button variant="destructive" disabled={isPending} onClick={handleArchive}>
        {isPending ? "Archiving…" : "Archive"}
      </Button>
    </DialogFooter>
  </DialogContent>
</Dialog>

Acceptance criteria

• ArchiveClientButton uses Dialog instead of window.confirm()
• AttachmentsList delete uses Dialog instead of window.confirm()
• CommentRow delete uses Dialog instead of window.confirm()
• No window.confirm() or window.alert() calls remain in the codebase
• npm run build passes