fix(nextcloud): NULL parent_id on cross-source-root child folders + spinner

The previous fix NULLed parent_id only for folders within the
SourceRoot being deleted, but folder rows under a *different*
SourceRoot whose path nests inside this one (e.g. 'Leóns 1st Year' at
.../Taco and Muli - 2024 onward/Leóns 1st Year) still pointed into
our delete set. folders_parent_id_fkey kept tripping. Widen the UPDATE
to NULL parent_id for any folder whose parent_id is in folder_ids,
regardless of source_root_id.

UI: trash button on a Nextcloud library now swaps to a spinning
Loader2 while the delete is in flight (only the row being deleted —
others stay as trash icons but disabled). Title updates to flag
that a cascade through every photo + folder can take a few seconds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/dialogs/SettingsDialog.tsx

@@ -1594,9 +1594,17 @@ function NextcloudIntegrationCard() {
                   variant="ghost"
                   disabled={removeRoot.isPending}
                   onClick={() => removeRoot.mutate(r.id)}
-                  title="Remove this library"
+                  title={
+                    removeRoot.isPending && removeRoot.variables === r.id
+                      ? 'Removing — cascades through every photo + folder, may take a few seconds'
+                      : 'Remove this library'
+                  }
                 >
-                  <Trash2 className="h-3 w-3" />
+                  {removeRoot.isPending && removeRoot.variables === r.id ? (
+                    <Loader2 className="h-3 w-3 animate-spin" />
+                  ) : (
+                    <Trash2 className="h-3 w-3" />
+                  )}
                 </Button>
               </li>
             ))}