fix: prevent static settings text selection

Disable text selection across the active Settings view and every related dialog while explicitly preserving selection inside editable fields and text areas. Add regression coverage for the selection scope and input exceptions.

src/renderer/App.tsx

@@ -4796,7 +4796,7 @@ export function App(): ReactElement {
 
   return (
     <div
-      className={`app-shell${dragOver ? " drag-over" : ""}`}
+      className={`app-shell${dragOver ? " drag-over" : ""}${tab === "settings" ? " settings-active" : ""}`}
       onDragEnter={(event) => {
         event.preventDefault();
         if (draggedPackageIdRef.current) { return; }