feat(db): 添加ops告警静默和错误分类优化迁移

- 添加ops告警静默功能的数据库结构
- 优化错误分类和重试结果字段标准化

backend/migrations/037_ops_alert_silences.sql

@@ -0,0 +1,28 @@
+-- +goose Up
+-- +goose StatementBegin
+-- Ops alert silences: scoped (rule_id + platform + group_id + region)
+
+CREATE TABLE IF NOT EXISTS ops_alert_silences (
+    id BIGSERIAL PRIMARY KEY,
+
+    rule_id BIGINT NOT NULL,
+    platform VARCHAR(64) NOT NULL,
+    group_id BIGINT,
+    region VARCHAR(64),
+
+    until TIMESTAMPTZ NOT NULL,
+    reason TEXT,
+
+    created_by BIGINT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_ops_alert_silences_lookup
+    ON ops_alert_silences (rule_id, platform, group_id, region, until);
+
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+DROP TABLE IF EXISTS ops_alert_silences;
+-- +goose StatementEnd