feat(dashboard): show Claude usage (tokens + requests) since server start

ClaudeBrain now returns per-reply token usage (Reply.usage from the API
response), the dashboard accumulates it (monitor.add_claude_usage), and the
header shows a "클로드 토큰" stat (input+output total, with a tooltip breaking
down input/output tokens and request count).

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

wsai/interfaces.py

@@ -63,6 +63,7 @@ class Reply:
 
     text: str
     ts: float
+    usage: dict | None = None  # Claude token usage for this reply, when known
 
 
 # --------------------------------------------------------------------------- #