Add initial backend implementation

- Go module with Gin, GORM, JWT, excelize dependencies
- Configuration loading from YAML with all settings
- GORM models for users, categories, components, configurations, alerts
- Repository layer for all entities
- Services: auth (JWT), pricing (median/average/weighted), components,
  quotes, configurations, export (CSV/XLSX), alerts
- Middleware: JWT auth, role-based access, CORS
- HTTP handlers for all API endpoints
- Main server with dependency injection and graceful shutdown

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/repository/stats.go

@@ -0,0 +1,92 @@
+package repository
+
+import (
+	"time"
+
+	"github.com/mchus/quoteforge/internal/models"
+	"gorm.io/gorm"
+)
+
+type StatsRepository struct {
+	db *gorm.DB
+}
+
+func NewStatsRepository(db *gorm.DB) *StatsRepository {
+	return &StatsRepository{db: db}
+}
+
+func (r *StatsRepository) GetByLotName(lotName string) (*models.ComponentUsageStats, error) {
+	var stats models.ComponentUsageStats
+	err := r.db.Where("lot_name = ?", lotName).First(&stats).Error
+	if err != nil {
+		return nil, err
+	}
+	return &stats, nil
+}
+
+func (r *StatsRepository) Upsert(stats *models.ComponentUsageStats) error {
+	return r.db.Save(stats).Error
+}
+
+func (r *StatsRepository) IncrementUsage(lotName string, quantity int, revenue float64) error {
+	now := time.Now()
+
+	result := r.db.Model(&models.ComponentUsageStats{}).
+		Where("lot_name = ?", lotName).
+		Updates(map[string]interface{}{
+			"quotes_total":    gorm.Expr("quotes_total + 1"),
+			"quotes_last_30d": gorm.Expr("quotes_last_30d + 1"),
+			"quotes_last_7d":  gorm.Expr("quotes_last_7d + 1"),
+			"total_quantity":  gorm.Expr("total_quantity + ?", quantity),
+			"total_revenue":   gorm.Expr("total_revenue + ?", revenue),
+			"last_used_at":    now,
+		})
+
+	if result.RowsAffected == 0 {
+		stats := &models.ComponentUsageStats{
+			LotName:       lotName,
+			QuotesTotal:   1,
+			QuotesLast30d: 1,
+			QuotesLast7d:  1,
+			TotalQuantity: quantity,
+			TotalRevenue:  revenue,
+			LastUsedAt:    &now,
+		}
+		return r.db.Create(stats).Error
+	}
+
+	return result.Error
+}
+
+func (r *StatsRepository) GetTopComponents(limit int) ([]models.ComponentUsageStats, error) {
+	var stats []models.ComponentUsageStats
+	err := r.db.
+		Order("quotes_last_30d DESC").
+		Limit(limit).
+		Find(&stats).Error
+	return stats, err
+}
+
+func (r *StatsRepository) GetTrendingComponents(limit int) ([]models.ComponentUsageStats, error) {
+	var stats []models.ComponentUsageStats
+	err := r.db.
+		Where("trend_direction = ? AND trend_percent > ?", models.TrendUp, 20).
+		Order("trend_percent DESC").
+		Limit(limit).
+		Find(&stats).Error
+	return stats, err
+}
+
+// ResetWeeklyCounters resets quotes_last_7d (run weekly via cron)
+func (r *StatsRepository) ResetWeeklyCounters() error {
+	return r.db.Model(&models.ComponentUsageStats{}).
+		Where("1 = 1").
+		Update("quotes_last_7d", 0).Error
+}
+
+// ResetMonthlyCounters resets quotes_last_30d (run monthly via cron)
+func (r *StatsRepository) ResetMonthlyCounters() error {
+	return r.db.Model(&models.ComponentUsageStats{}).
+		Where("1 = 1").
+		Update("quotes_last_30d", 0).Error
+}