Depends on WT-18394. Wire WT repair to trigger verify with fix_btree_size enabled, so repair actually corrects a stale btree size instead of just warning about it. This is the intended enforcement point — the config is only meant to be turned on through repair, and is exposed as a verify config mainly so it's testable in isolation. Add a test that builds a database with an incorrect metadata size, runs repair, and confirms the size is corrected and logged.