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/backends/claude.py

@@ -176,4 +176,9 @@ class ClaudeBrain:
             messages=msgs,
         )
         text = "".join(b.text for b in resp.content if b.type == "text")
-        return Reply(text=text.strip(), ts=time.monotonic())
+        usage = None
+        u = getattr(resp, "usage", None)
+        if u is not None:
+            usage = {"input": getattr(u, "input_tokens", 0) or 0,
+                     "output": getattr(u, "output_tokens", 0) or 0}
+        return Reply(text=text.strip(), ts=time.monotonic(), usage=usage)