feat: 个人用户聚合视图 — 客户管理双Tab+四模块数据聚合

- customers 表新增 customer_type 列 (unit/individual)
- 客户管理页：单位客户 | 个人用户 Tab 切换
- 个人用户 Tab: 直接内嵌4 Tab 显示所有个人用户的聚合数据
- 个人用户通过业务模块快速新建产生 (customer_type=individual)
- 4个业务API新增 customer_type 筛选参数（JOIN customers）
- 客户列表排序: 个人用户置顶

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

backend/app/schemas/customer.py

@@ -45,6 +45,7 @@ class ContactOut(BaseModel):
 # ── Customer ──
 class CustomerCreate(BaseModel):
     name: str
+    customer_type: str = "unit"
     industry: str = ""
     address: str = ""
     in_use_services: str = ""
@@ -56,6 +57,7 @@ class CustomerCreate(BaseModel):
 
 class CustomerUpdate(BaseModel):
     name: Optional[str] = None
+    customer_type: Optional[str] = None
     industry: Optional[str] = None
     address: Optional[str] = None
     in_use_services: Optional[str] = None
@@ -67,6 +69,7 @@ class CustomerUpdate(BaseModel):
 class CustomerOut(BaseModel):
     id: uuid.UUID
     name: str
+    customer_type: str = "unit"
     industry: str
     address: str
     in_use_services: str
@@ -84,6 +87,7 @@ class CustomerOut(BaseModel):
 class CustomerListOut(BaseModel):
     id: uuid.UUID
     name: str
+    customer_type: str = "unit"
     industry: str
     in_use_services: str
     primary_manager_name: Optional[str] = None