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/api/src/plugins/mcp/mcp_bridge.py

@@ -18,6 +18,8 @@ import re
 import uuid
 from dataclasses import dataclass, field
 from datetime import datetime
+
+from src.utils.timezone import now_taipei
 from enum import Enum
 from typing import Any
 
@@ -53,7 +55,7 @@ class MCPToolResult:
     output: Any | None = None
     error: str | None = None
     duration: float = 0.0
-    timestamp: datetime = field(default_factory=datetime.utcnow)
+    timestamp: datetime = field(default_factory=now_taipei)
 
     def to_dict(self) -> dict:
         return {
@@ -390,7 +392,7 @@ class MCPBridge:
             MCPToolResult (符合 ActionResult 介面)
         """
         execution_id = str(uuid.uuid4())
-        start_time = datetime.utcnow()
+        start_time = now_taipei()
 
         try:
             # ========================================
@@ -494,7 +496,7 @@ class MCPBridge:
 
     def _calc_duration(self, start_time: datetime) -> float:
         """計算執行時間 (毫秒)"""
-        return (datetime.utcnow() - start_time).total_seconds() * 1000
+        return (now_taipei() - start_time).total_seconds() * 1000
 
     # ==================== ActionExecutor 介面對齊 ====================