Fix popup: use JS dialog outside Blazor DOM tree

Previous fix removed the JS DOM portal but kept the dialog in Blazor's
render tree. The overlay showed but the dialog was clipped/invisible
due to ancestor overflow constraints that position:fixed alone can't
escape in WebView with scoped CSS.

Adopt the approach from PR #226: render the close-confirmation dialog
entirely via JS (window.showCloseSessionDialog), creating DOM elements
imperatively and appending to document.body. Blazor never tracks these
elements, so no render batch desync on open/close/delete.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: PureWeen

PolyPilot/Components/Layout/SessionListItem.razor

@@ -5,7 +5,6 @@
 @inject RepoManager RepoManager
 @inject IJSRuntime JS
 
-
 @{
     var isPinned = Meta?.IsPinned ?? false;
     var sessionDir = GetSessionDirectory();