fix(db): C1 時區統一遷移 — utc_now → taipei_now (全 5 table)

🔴 首席架構師審查 C1: 全系統禁止 UTC，必須台北時區 +8

- utc_now() → taipei_now() (調用 src.utils.timezone.now_taipei)
- 影響: ApprovalRecord, TimelineEvent, AuditLog, IncidentRecord, KnowledgeEntryRecord
- 13 處 default/onupdate 全部替換
- 移除 datetime.UTC import

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/api/src/db/models.py

@@ -10,7 +10,7 @@ Schema 設計原則：
 - 索引優化查詢
 """
 
-from datetime import UTC, datetime
+from datetime import datetime
 from typing import Any
 from uuid import uuid4
 
@@ -36,9 +36,14 @@ from src.models.knowledge import EntrySource, EntryStatus, EntryType
 # Helper Functions
 # =============================================================================
 
-def utc_now() -> datetime:
-    """Get current UTC datetime"""
-    return datetime.now(UTC)
+def taipei_now() -> datetime:
+    """取得台北時區當前時間 (UTC+8)
+
+    🔴 HARD RULE: 全系統使用台北時區，禁止 UTC
+    2026-04-02 Claude Code: C1 時區統一遷移 (首席架構師審查)
+    """
+    from src.utils.timezone import now_taipei
+    return now_taipei()
 
 
 def generate_uuid() -> str:
@@ -114,7 +119,7 @@ class ApprovalRecord(Base):
     # 最後觸發時間 - 同指紋告警最近一次出現的時間
     last_seen_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
         nullable=False,
         comment="Last time this alert pattern was seen",
     )
@@ -122,12 +127,12 @@ class ApprovalRecord(Base):
     # Timestamps
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
     )
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
-        onupdate=utc_now,
+        default=taipei_now,
+        onupdate=taipei_now,
     )
     expires_at: Mapped[datetime | None] = mapped_column(
         DateTime(timezone=True),
@@ -200,7 +205,7 @@ class TimelineEvent(Base):
     # Timestamp
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
     )
 
     # Indexes
@@ -324,7 +329,7 @@ class AuditLog(Base):
     # Timestamps
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
     )
 
     # Indexes
@@ -417,13 +422,13 @@ class IncidentRecord(Base):
     # === 時間軸 ===
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
         nullable=False,
     )
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
-        onupdate=utc_now,
+        default=taipei_now,
+        onupdate=taipei_now,
         nullable=False,
     )
     resolved_at: Mapped[datetime | None] = mapped_column(
@@ -537,12 +542,12 @@ class KnowledgeEntryRecord(Base):
     created_by: Mapped[str | None] = mapped_column(String(100), nullable=True)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
+        default=taipei_now,
     )
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
-        default=utc_now,
-        onupdate=utc_now,
+        default=taipei_now,
+        onupdate=taipei_now,
     )
 
     # Indexes