fix(libsync): rename OWNCLOUD_BULK_UPLOAD to NEXTCLOUD_BULK_UPLOAD

Per review feedback from @mgallien on PR #10300 - new env vars should
use the NEXTCLOUD_ prefix, not the legacy OWNCLOUD_ one (kept only for
the pre-existing OWNCLOUD_CHUNKING_NG override).

Signed-off-by: mosandlt <10558666+mosandlt@users.noreply.github.com>
Assisted-by: ClaudeCode:claude-sonnet-5

Author: mosandlt

src/libsync/capabilities.cpp

@@ -232,7 +232,7 @@ int Capabilities::maxConcurrentChunkUploads() const
 
 bool Capabilities::bulkUpload() const
 {
-    static const auto bulkUploadEnv = qgetenv("OWNCLOUD_BULK_UPLOAD");
+    static const auto bulkUploadEnv = qgetenv("NEXTCLOUD_BULK_UPLOAD");
     if (bulkUploadEnv == "0")
         return false;
     if (bulkUploadEnv == "1")