fix(voice): stop backtick TTS crash and actually count error turns

Claude replies with markdown/backticks by default; MeloTTS's Korean text
normaliser has no entry for '`' and dies with KeyError: '`', so any reply
mentioning a command/code block crashed the whole voice turn (500 on
/api/voice-turn). Fix at the shared synth() choke point with
normalize_for_speech(), which flattens code fences/inline code/links/markdown
and guarantees no backtick reaches the worker — covering both the dashboard
voice turn and the Discord speak() bridge. Also add a PERSONA line asking the
model to avoid markdown (belt-and-suspenders; the code strip is the real fix).

errors_total never moved for turn-level failures: it was only bumped by
log("error") events, and the dashboard voice path calls turn.finish(error=...)
without logging. Emit one error-level log event from Turn.finish() when a turn
ends in error, so both the server counter and the browser SSE mirror stay
consistent, guarded to count at most once. Drop the now-redundant pipeline
log("error") to avoid double counting and remove the dead _publish stub.

Verified: raw backtick -> worker KeyError '`' reproduced; after fix real
MeloTTS synth of a backtick+fenced reply succeeds; /api/voice-turn returns 200
with a wav body on a backtick reply and errors_total stays 0, and an induced
synth failure returns 500 with errors_total incrementing to exactly 1. Full
suite 18 passed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

wsai/backends/claude.py

@@ -125,7 +125,8 @@ class ClaudeBrain:
     PERSONA = (
         "너는 사용자의 디스코드 화면공유를 실시간으로 함께 보는 AI 파트너야. "
         "화면 설명을 참고해 자연스러운 반말/존댓말은 사용자에 맞추고, 짧고 대화하듯 답해. "
-        "화면을 못 봤으면 솔직히 말해."
+        "화면을 못 봤으면 솔직히 말해. "
+        "네 답변은 음성으로 읽히니 마크다운·코드블록·백틱 같은 서식 없이 평범한 말로만 답해."
     )
 
     def __init__(self, *, model: str = "claude-sonnet-4-5", api_key: str | None = None) -> None: