feat: 添加用户记账连击（streak）功能，包括服务、处理器、模型和仓库层。

internal/repository/streak_repository.go

@@ -107,3 +107,51 @@ func (r *StreakRepository) GetTransactionDatesInRange(userID uint, startDate, en
 
 	return dates, nil
 }
+
+// GetDailyContribution returns daily transaction counts in a date range
+func (r *StreakRepository) GetDailyContribution(userID uint, startDate, endDate time.Time) ([]models.DailyContribution, error) {
+	var results []models.DailyContribution
+
+	// SQLite uses strftime, MySQL/Postgres uses DATE()
+	// Using a more generic approach compatible with SQLite (which is likely used locally)
+	// For production readiness with multiple DBs, raw SQL might be safer or check dialect
+
+	rows, err := r.db.Model(&models.Transaction{}).
+		Select("DATE(transaction_date) as date, COUNT(*) as count").
+		Where("user_id = ? AND transaction_date >= ? AND transaction_date <= ?", userID, startDate, endDate).
+		Group("DATE(transaction_date)").
+		Order("date ASC").
+		Rows()
+
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var dateStr string // Using string to handle potential format differences
+		var count int
+		// Scan into generic types then convert
+		// Some drivers return date as time.Time, some as string/bytes
+		// Let's try scan into string first (common for DATE() function result)
+		// Or scan into interface{} to be safe
+		if err := rows.Scan(&dateStr, &count); err != nil {
+			// If string scan fails, try time.Time
+			// Unfortunately we can't rewind rows. scan is one-way.
+			// But usually drivers handle string conversion for DATE()
+			// If this fails we might need to adjust based on specific DB driver
+			return nil, err
+		}
+		// Normalize date string to YYYY-MM-DD (take first 10 chars if it includes time)
+		if len(dateStr) > 10 {
+			dateStr = dateStr[:10]
+		}
+
+		results = append(results, models.DailyContribution{
+			Date:  dateStr,
+			Count: count,
+		})
+	}
+
+	return results, nil
+}