feat(health): 新增 critical_alerts + critical_alert_responses 表 + Entity

危急值告警数据模型：status(pending/acknowledged/resolved/escalated)、
escalation_level 分级升级、乐观锁、软删除。

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

@@ -89,6 +89,7 @@ mod m20260427_000086_enable_rls_all_tables;
 mod m20260427_000087_audit_logs_hash_chain;
 mod m20260428_000088_rls_policy_strict;
 mod m20260428_000089_blind_indexes;
+mod m20260428_000090_critical_alerts;
 
 pub struct Migrator;
 
@@ -185,6 +186,7 @@ impl MigratorTrait for Migrator {
             Box::new(m20260427_000087_audit_logs_hash_chain::Migration),
             Box::new(m20260428_000088_rls_policy_strict::Migration),
             Box::new(m20260428_000089_blind_indexes::Migration),
+            Box::new(m20260428_000090_critical_alerts::Migration),
         ]
     }
 }