feat(report): 报表统计四表查询与 Excel 签字导出

- 四表接口 /api/v1/reports/*：个人明细（全筛选 summary）、部门汇总（团队基数与月结聚合同源、12.5%/5% 分列、零行经理、冻结对照）、业务统计（排除聚合行）、回款统计（8 档区间恒在、回款金额按 receipt_id 去重防分摊拆行翻倍）
- Excel 导出：公司页眉/财务复核栏/领导签字栏/日期/版本、Decimal 原值 + number_format、文本防公式注入、2 万行超限 400、导出行为入操作日志
- manager_share 共享模块：月结聚合与报表部门汇总同源取参与分桶（薄委托保留测试入口）
- 区间元数据落 core/report_meta（repository 需要类型，避免反向依赖 service 层）
- 准入 require_roles(admin/finance/leader)，支持自定义 403 文案

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

backend/app/api/router.py

@@ -16,6 +16,7 @@ from app.api.v1.business import ratings as business_ratings
 from app.api.v1.business import receipts as business_receipts
 from app.api.v1.business import shipments as business_shipments
 from app.api.v1.calc import router as calc_router
+from app.api.v1.reports import router as reports_router
 from app.api.v1.settlements import router as settlements_router
 from app.api.v1.system import approvals as system_approvals
 from app.api.v1.system import business_roles as system_business_roles
@@ -65,5 +66,7 @@ v1_router.include_router(business_router)
 v1_router.include_router(calc_router)
 # 月度结算（M3 ④）：/api/v1/settlements/*，读登录即可、写限管理员与营销后勤
 v1_router.include_router(settlements_router)
+# 报表统计（M4 ⑤）：/api/v1/reports/*，只读，限管理员/财务/领导
+v1_router.include_router(reports_router)
 
 api_router.include_router(v1_router)