feat(health): 班次管理与护士分配 — Shift/PatientAssignment/HandoffLog CRUD

- 新增 3 张数据表迁移 (shifts, patient_assignments, shift_handoff_log)
- 3 个 SeaORM Entity (shift, patient_assignment, handoff_log)
- 完整 CRUD 服务层：班次管理、患者分配（含批量分配）、交接记录
- 12 个 API 端点 + health.shifts.list/manage 权限
- 班次列表含患者分配摘要 (patient_count/critical_count/attention_count)
- 乐观锁、软删除、审计日志、事件发布
- 输入验证：period/shift_status/care_level 白名单

crates/erp-server/migration/src/lib.rs

@@ -111,6 +111,7 @@ mod m20260504_000108_alter_vital_signs_hourly_add_soft_delete;
 mod m20260504_000109_add_missing_fk_constraints;
 mod m20260504_000110_alter_critical_alerts_version_i32;
 mod m20260505_000111_create_care_plan;
+mod m20260505_000112_create_shift_management;
 
 pub struct Migrator;
 
@@ -229,6 +230,7 @@ impl MigratorTrait for Migrator {
             Box::new(m20260504_000109_add_missing_fk_constraints::Migration),
             Box::new(m20260504_000110_alter_critical_alerts_version_i32::Migration),
             Box::new(m20260505_000111_create_care_plan::Migration),
+            Box::new(m20260505_000112_create_shift_management::Migration),
         ]
     }
 }