chore(submodule): bump ephapax → ef9c91f (PR #35 — zero Admitted, full preservation)

PR #35 closes the preservation theorem completely:
- region_env_perm_typing: transfers typing across equivalent region envs
- region_add_typing: adding a region preserves typing
- preservation: Qed (was 2× Admitted)
Result: 0 Admitted, 62 Qed across formal/Semantics.v

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hyperpolymath