feat(ugc): staff reprocessing of a property goes to the front of the queue

/reprocessproperty and the dashboard's Reprocess all models mark the
property's models as priority (ugc.priority, migrations mysql 94 and sqlite
77). The UGC server takes priority models first, polls them even when its
queue is full, and puts them at its front, as it does cars and rockets. The
flag clears once a model is made.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dUgcServer/UgcProcessor.h

@@ -157,6 +157,7 @@ private:
 		bool iconOnly{};                // a model's icon drawn again from its stored .nif
 		bool assembly{};                // with `preview`: answered with the assembled .nif instead of an icon
 		UgcIconParams::Values iconValues; // models: the preset and override (UgcIconParams)
+		bool priority{};                // models staff asked to be made again: queued at the front
 	};
 
 	// A written file's MD5 and size as the client has it after inflating it (from its .checksum)