feat(chat): NemoClaw Claude API 加 token+費用統計

Claude Haiku 4.5: Input $0.80/1M, Output $4.00/1M
每次回覆顯示: token 數 | 本次費用 | 本月累計
Redis key: claude_cost:YYYY-MM，TTL 40 天

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/services/chat_manager.py

@@ -176,7 +176,30 @@ class ChatManager:
                 )
                 resp.raise_for_status()
                 data = resp.json()
-                return data["content"][0]["text"].strip()
+                text = data["content"][0]["text"].strip()
+
+                # Token/費用統計 — Claude Haiku 4.5: Input $0.80/1M, Output $4.00/1M
+                usage = data.get("usage", {})
+                in_tok = usage.get("input_tokens", 0)
+                out_tok = usage.get("output_tokens", 0)
+                cost = (in_tok * 0.0000008) + (out_tok * 0.000004)
+
+                # 月累計到 Redis
+                from src.core.redis_client import get_redis
+                from src.utils.timezone import now_taipei
+                redis = get_redis()
+                month_key = f"claude_cost:{now_taipei().strftime('%Y-%m')}"
+                try:
+                    current = float(await redis.get(month_key) or 0)
+                    new_total = current + cost
+                    await redis.set(month_key, str(round(new_total, 6)), ex=40 * 24 * 3600)
+                except Exception:
+                    new_total = cost
+
+                logger.info("nemotron_claude_usage", in_tokens=in_tok, out_tokens=out_tok,
+                            cost_usd=round(cost, 6), monthly_total_usd=round(new_total, 4))
+
+                return f"{text}\n\n<i>📊 {in_tok+out_tok} tokens | ${cost:.4f} | 本月累計 ${new_total:.4f}</i>"
         except Exception as e:
             logger.warning("nemotron_chat_failed", error=str(e))
             return None