feat(ugc): when each creation was made and how long it took, on the UGC page

The UGC server records how long each successful make took (process_ms on
ugc and ugc_modular_build; migrations sqlite 73, mysql 90). The UGC page
shows it with the time it was made: in the models list's Made column
(sortable, slowest first), in the tiles' tooltips, in the item preview
and in an assembly's References. The gallery can sort by slowest to
make too. Makes from before this are shown without a duration.

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

migrations/dlu/sqlite/73_ugc_process_time.sql

@@ -0,0 +1,3 @@
+/* UGC server: how long it took to make each model and car or rocket build. See the MySQL migration. */
+ALTER TABLE ugc ADD COLUMN process_ms INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE ugc_modular_build ADD COLUMN process_ms INTEGER NOT NULL DEFAULT 0;