fix: 修复复审2个建议 (models注释 + N+1查询 + 事务边界)

- models.py: 注释中旧模式名对齐 EditingMode 枚举
- list_by_user: 批量加载 segments 避免 N+1 查询
- create(): flush 替代 commit，create_segments 统一提交事务

packages/adapters/sqlalchemy_impl/models.py

@@ -287,7 +287,7 @@ class TemplateModel(Base):
     id = Column(String(36), primary_key=True)
     user_id = Column(String(36), nullable=False, index=True)
     name = Column(String(200), nullable=False)
-    mode = Column(String(30), nullable=False, index=True)  # pip / person_narration / one_take / voice_over_mix
+    mode = Column(String(30), nullable=False, index=True)  # EditingMode 枚举值: pip / voice_pip / one_take / voice_over
     category = Column(String(100), nullable=False, default="")
     tags = Column(JSON, nullable=False, default=list)
     title_config = Column(JSON, nullable=False, default=dict)
@@ -307,7 +307,7 @@ class TemplateSegmentModel(Base):
     segment_order = Column(Integer, nullable=False)
     duration_min = Column(Float, nullable=False)
     duration_max = Column(Float, nullable=False)
-    material_type = Column(String(20), nullable=True)  # 仅 voice_over_mix: 人物/场景
+    material_type = Column(String(20), nullable=True)  # 仅 voice_over 模式: 人物/场景
     created_at = Column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))
     updated_at = Column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))