fix(transport): flush folders before resolving template FolderId FKs

ApplyTemplateFoldersAsync staged new folders via AddFolderAsync but
never called SaveChanges -- so on relational providers (MSSQL) the
new folders sit in the change tracker with Id=0 until the outer
SaveChanges much later in ApplyAsync. The previous attempt to read
the folder name->id map via _templateRepo.GetAllFoldersAsync only
saw pre-existing rows, so newly-bundled folders couldn't satisfy a
template's FolderName reference. Add an intermediate SaveChanges
inside ApplyTemplatesAsync before the folder query.

src/ScadaLink.Transport/Import/BundleImporter.cs

@@ -822,9 +822,14 @@ public sealed class BundleImporter : IBundleImporter
         var stubs = await _templateRepo.GetAllTemplatesAsync(ct).ConfigureAwait(false);
         var byName = stubs.ToDictionary(t => t.Name, t => t, StringComparer.Ordinal);
 
-        // ApplyTemplateFoldersAsync has already flushed every imported folder
-        // (and target folders pre-exist), so name-keyed lookup resolves to the
-        // persisted FolderId every imported template should reference.
+        // Folder ids must be materialised before we wire templates' FolderId
+        // FKs. ApplyTemplateFoldersAsync staged the rows via AddFolderAsync
+        // but did NOT call SaveChanges -- on a relational provider that means
+        // every new folder still has Id=0 in the change tracker. Flushing
+        // here is safe: we're inside the outer import transaction (begun in
+        // ApplyAsync), so any later throw still rolls everything back as one
+        // unit. The cost is one extra round-trip per import, negligible.
+        await _dbContext.SaveChangesAsync(ct).ConfigureAwait(false);
         var folders = await _templateRepo.GetAllFoldersAsync(ct).ConfigureAwait(false);
         var folderIdByName = folders.ToDictionary(f => f.Name, f => f.Id, StringComparer.Ordinal);