feat(scheduler): 引入调度快照缓存与 outbox 回放

- 调度热路径优先读 Redis 快照，保留分组排序语义
- outbox 回放 + 全量重建纠偏，失败重试不推进水位
- 自动 Atlas 基线对齐并同步调度配置示例

backend/internal/repository/scheduler_outbox_repo.go

@@ -0,0 +1,96 @@
+package repository
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+type schedulerOutboxRepository struct {
+	db *sql.DB
+}
+
+func NewSchedulerOutboxRepository(db *sql.DB) service.SchedulerOutboxRepository {
+	return &schedulerOutboxRepository{db: db}
+}
+
+func (r *schedulerOutboxRepository) ListAfter(ctx context.Context, afterID int64, limit int) ([]service.SchedulerOutboxEvent, error) {
+	if limit <= 0 {
+		limit = 100
+	}
+	rows, err := r.db.QueryContext(ctx, `
+		SELECT id, event_type, account_id, group_id, payload, created_at
+		FROM scheduler_outbox
+		WHERE id > $1
+		ORDER BY id ASC
+		LIMIT $2
+	`, afterID, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		_ = rows.Close()
+	}()
+
+	events := make([]service.SchedulerOutboxEvent, 0, limit)
+	for rows.Next() {
+		var (
+			payloadRaw []byte
+			accountID  sql.NullInt64
+			groupID    sql.NullInt64
+			event      service.SchedulerOutboxEvent
+		)
+		if err := rows.Scan(&event.ID, &event.EventType, &accountID, &groupID, &payloadRaw, &event.CreatedAt); err != nil {
+			return nil, err
+		}
+		if accountID.Valid {
+			v := accountID.Int64
+			event.AccountID = &v
+		}
+		if groupID.Valid {
+			v := groupID.Int64
+			event.GroupID = &v
+		}
+		if len(payloadRaw) > 0 {
+			var payload map[string]any
+			if err := json.Unmarshal(payloadRaw, &payload); err != nil {
+				return nil, err
+			}
+			event.Payload = payload
+		}
+		events = append(events, event)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return events, nil
+}
+
+func (r *schedulerOutboxRepository) MaxID(ctx context.Context) (int64, error) {
+	var maxID int64
+	if err := r.db.QueryRowContext(ctx, "SELECT COALESCE(MAX(id), 0) FROM scheduler_outbox").Scan(&maxID); err != nil {
+		return 0, err
+	}
+	return maxID, nil
+}
+
+func enqueueSchedulerOutbox(ctx context.Context, exec sqlExecutor, eventType string, accountID *int64, groupID *int64, payload any) error {
+	if exec == nil {
+		return nil
+	}
+	var payloadJSON []byte
+	if payload != nil {
+		encoded, err := json.Marshal(payload)
+		if err != nil {
+			return err
+		}
+		payloadJSON = encoded
+	}
+	_, err := exec.ExecContext(ctx, `
+		INSERT INTO scheduler_outbox (event_type, account_id, group_id, payload)
+		VALUES ($1, $2, $3, $4)
+	`, eventType, accountID, groupID, payloadJSON)
+	return err
+}