[ITEP-91238] Fix: autocalibration updateMapProcessed fails with HTTP 400

[dmytroye]

📝 Description

Fix: autocalibration updateMapProcessed fails with HTTP 400

SceneSerializer.validate() introduced in #1337 unconditionally required name in all scene updates. Autocalibration's updateMapProcessed sends only {'map_processed': <timestamp>} with no name, causing every markerless calibration to fail with a 400 after hloc feature export.

Change: Guard the name check by creation vs. partial-update context — require name only when creating a scene; on partial updates, only validate it if it was actually provided in the request.

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[saratpoluri]

With this PR merged: #1278, this won't be needed.