feat(pl): 运费结算审批分流与车辆挂车号等 PL 能力完善

拆分运费审批/出款页面，补充结算发票附件与菜单 SQL，并同步前后端模型与车辆相关展示。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/models/pl_models.py

@@ -56,6 +56,7 @@ class PlVehicle(Base):
     carrier_id = Column(String(64), nullable=True, comment="承运商ID（类型为承运商时必填）")
     carrier_name = Column(String(200), nullable=True, comment="承运商名称（冗余）")
     license_plate = Column(String(20), nullable=False, unique=True, comment="车牌号")
+    trailer_no = Column(String(20), nullable=True, comment="挂车号")
     default_driver_id = Column(String(64), nullable=True, comment="默认司机ID")
     default_driver_name = Column(String(100), nullable=True, comment="默认司机姓名（冗余）")
     load_capacity = Column(DECIMAL(10, 2), nullable=True, comment="载重（吨）")
@@ -533,6 +534,7 @@ class PlFreightSettlement(Base):
     # 发票信息
     invoice_no = Column(String(50), nullable=True, comment="发票号")
     invoice_date = Column(Date, nullable=True, comment="开票日期")
+    invoice_attachment_urls = Column(Text, nullable=True, comment="发票附件URLs，逗号分隔")
 
     # 结算状态
     settlement_status = Column(String(20), nullable=False, default="pending", comment="结算状态 pending-待提交 submitted-已提交 approved-审核通过 confirmed-已确认")