feat(api): 統一使用台北時區 UTC+8 (禁止 UTC)

- 新增 src/utils/timezone.py 時區工具函式
- 修改 11 個後端檔案，全部改用 now_taipei()
- 更新 HARD_RULES.md 加入時區鐵律章節
- 更新 Skills 02/04 加入時區禁令

🔴 HARD RULE: 禁止 datetime.utcnow() / datetime.now(UTC)
✅ 正確做法: from src.utils.timezone import now_taipei

Memory: feedback_timezone_taipei.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/sensor/agent.py

@@ -32,7 +32,10 @@ import random
 import socket
 import sys
 import time
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
+
+# 台北時區 (UTC+8) - 系統統一時區
+TAIPEI_TZ = timezone(timedelta(hours=8))
 from typing import Any
 from uuid import uuid4
 
@@ -160,7 +163,7 @@ class SensorAgent:
             return None
 
         # 建立標準 Signal 格式
-        now = datetime.now(timezone.utc)
+        now = datetime.now(TAIPEI_TZ)
         signal = {
             "alert_name": alert.get("alert_name", "UnknownAlert"),
             "severity": alert.get("severity", "warning"),
@@ -261,7 +264,7 @@ def main() -> int:
     print("=" * 70)
     print("AWOOOI Sensor Agent - Phase 6.5 神經末梢")
     print("=" * 70)
-    print(f"Time: {datetime.now().isoformat()}")
+    print(f"Time: {datetime.now(TAIPEI_TZ).isoformat()}")
     print(f"Host: {socket.gethostname()}")
     print()