New DictionaryPlugin with !antonym, !pronounce, !etymology, !difficulty,
and !rhyme commands. Integrate antonyms into !define (concurrent 500ms
fetch), difficulty tier into Hangman headers, and etymology into WOTD.
Fix rhyme limit bug (request 50, display 7), variable shadowing, and
add spec-required emoji prefixes to all dictionary command outputs.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
