fix: 订单明细迁移补全 + 全局异常处理 + Vue 模板修复

- 新增迁移 20260531_0001 补全 sales_order_item 报价快照列（幂等）
- 添加全局未捕获异常处理器，500 错误返回具体异常信息并记录 traceback
- 修复 web-sales LoginPage 和 CustomersPage 中 import 语句误写在 <template> 内的问题

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/main.py

@@ -4,6 +4,9 @@
 启动命令: uvicorn backend.app.main:app --reload
 """
 
+import logging
+import traceback
+
 from fastapi import FastAPI
 from fastapi import Request
 from fastapi.middleware.cors import CORSMiddleware
@@ -13,6 +16,8 @@ from backend.app.api.routes import api_router
 from backend.app.core.config import get_settings
 from backend.app.core.exceptions import AppException
 
+logger = logging.getLogger(__name__)
+
 settings = get_settings()
 
 app = FastAPI(title=settings.app_name)
@@ -44,5 +49,22 @@ async def app_exception_handler(_: Request, exc: AppException) -> JSONResponse:
     )
 
 
+@app.exception_handler(Exception)
+async def unhandled_exception_handler(_: Request, exc: Exception) -> JSONResponse:
+    """捕获所有未处理异常，记录完整 traceback 到日志并返回 500。
+
+    避免 FastAPI 默认的 bare 500 响应，让运维能从日志中定位问题。
+    """
+    logger.error("Unhandled exception: %s\n%s", exc, traceback.format_exc())
+    return JSONResponse(
+        status_code=500,
+        content={
+            "code": 500,
+            "message": f"服务器内部错误: {type(exc).__name__}: {exc}",
+            "data": {},
+        },
+    )
+
+
 # 挂载所有 API 路由，路由前缀在 router.py 中统一定义
 app.include_router(api_router)

backend/migrations/versions/20260531_0001_add_pricing_snapshot_to_order_item.py

@@ -0,0 +1,45 @@
+"""add pricing snapshot columns to sales_order_item
+
+These columns may already exist in some environments (added manually).
+Each add_column is wrapped to tolerate DuplicateColumn gracefully.
+"""
+
+from alembic import op
+import sqlalchemy as sa
+from pymysql import err as pymysql_err
+
+revision = "20260531_0001"
+down_revision = "20260530_0001"
+branch_labels = None
+depends_on = None
+
+_COLUMNS = [
+    ("pricing_type", sa.Column("pricing_type", sa.String(length=32), nullable=True)),
+    ("length_m", sa.Column("length_m", sa.Numeric(10, 4), nullable=True)),
+    ("width_m", sa.Column("width_m", sa.Numeric(10, 4), nullable=True)),
+    ("area_sqm", sa.Column("area_sqm", sa.Numeric(18, 4), nullable=True)),
+    ("surcharge_detail", sa.Column("surcharge_detail", sa.Text(), nullable=True)),
+    ("processing_detail", sa.Column("processing_detail", sa.Text(), nullable=True)),
+    ("supplier_id", sa.Column("supplier_id", sa.Integer(), nullable=True)),
+    ("supplier_model", sa.Column("supplier_model", sa.String(length=64), nullable=True)),
+    ("price_tier", sa.Column("price_tier", sa.String(length=32), nullable=True)),
+]
+
+
+def upgrade() -> None:
+    for name, col in _COLUMNS:
+        try:
+            op.add_column("sales_order_item", col)
+        except Exception as exc:
+            if "Duplicate column" in str(exc):
+                pass
+            else:
+                raise
+
+
+def downgrade() -> None:
+    for name, _ in reversed(_COLUMNS):
+        try:
+            op.drop_column("sales_order_item", name)
+        except Exception:
+            pass

frontend/web-sales/src/views/CustomersPage.vue

@@ -4,8 +4,6 @@
   支持创建新客户（姓名、手机号必填），表格数据响应式适配移动端卡片布局。
 -->
 <template>
-import { useToast } from "../composables/useToast";
-const toast = useToast();
   <section class="page">
 <!--    <div class="page-hero">-->
 <!--      <div>-->
@@ -105,6 +103,9 @@ const toast = useToast();
 import { computed, onMounted, reactive, ref } from "vue";
 
 import { createCustomer, fetchCustomersPage } from "../mockApi";
+import { useToast } from "../composables/useToast";
+
+const toast = useToast();
 
 /** 数据加载状态 */
 const loading = ref(true);

frontend/web-sales/src/views/LoginPage.vue

@@ -4,8 +4,6 @@
   左侧展示系统介绍信息，右侧为登录卡片，已登录时自动跳转。
 -->
 <template>
-import { useToast } from "../composables/useToast";
-const toast = useToast();
   <section class="login-shell">
     <div class="hero-panel">
       <span class="eyebrow">Sales Workbench</span>