fix(analytics): 命中表索引幂等守卫独立+created_at 去掉 onupdate 语义

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

yunke-server/app/db/models.py

@@ -838,7 +838,11 @@ class SensitiveWord(Base):
     exclude_words: Mapped[list[Any] | dict[str, Any] | None] = mapped_column(
         JSON, nullable=True
     )
-    created_at: Mapped[dt.datetime] = _updated_at()
+    # created_at 不用 _updated_at():无 onupdate,首次落库后不被静默重写
+    # (T8 改词/T10 处置命中只该动 updated_at/disposition)
+    created_at: Mapped[dt.datetime] = mapped_column(
+        sa.DateTime, nullable=False, server_default=sa.func.now()
+    )
     updated_at: Mapped[dt.datetime] = _updated_at()
 
 
@@ -866,7 +870,11 @@ class SensitiveHit(Base):
     disposition: Mapped[str] = mapped_column(
         String(16), nullable=False, default="pending", server_default="pending"
     )
-    created_at: Mapped[dt.datetime] = _updated_at()
+    # created_at 不用 _updated_at():无 onupdate,首次落库后不被静默重写
+    # (T8 改词/T10 处置命中只该动 updated_at/disposition)
+    created_at: Mapped[dt.datetime] = mapped_column(
+        sa.DateTime, nullable=False, server_default=sa.func.now()
+    )
 
     __table_args__ = (
         sa.UniqueConstraint("word_id", "msg_id", name="uq_sensitive_hit_word_msg"),