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/alert.go

@@ -0,0 +1,91 @@
+package repository
+
+import (
+	"github.com/mchus/quoteforge/internal/models"
+	"gorm.io/gorm"
+)
+
+type AlertRepository struct {
+	db *gorm.DB
+}
+
+func NewAlertRepository(db *gorm.DB) *AlertRepository {
+	return &AlertRepository{db: db}
+}
+
+func (r *AlertRepository) Create(alert *models.PricingAlert) error {
+	return r.db.Create(alert).Error
+}
+
+func (r *AlertRepository) GetByID(id uint) (*models.PricingAlert, error) {
+	var alert models.PricingAlert
+	err := r.db.First(&alert, id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &alert, nil
+}
+
+func (r *AlertRepository) Update(alert *models.PricingAlert) error {
+	return r.db.Save(alert).Error
+}
+
+type AlertFilter struct {
+	Status   models.AlertStatus
+	Severity models.AlertSeverity
+	Type     models.AlertType
+	LotName  string
+}
+
+func (r *AlertRepository) List(filter AlertFilter, offset, limit int) ([]models.PricingAlert, int64, error) {
+	var alerts []models.PricingAlert
+	var total int64
+
+	query := r.db.Model(&models.PricingAlert{})
+
+	if filter.Status != "" {
+		query = query.Where("status = ?", filter.Status)
+	}
+	if filter.Severity != "" {
+		query = query.Where("severity = ?", filter.Severity)
+	}
+	if filter.Type != "" {
+		query = query.Where("alert_type = ?", filter.Type)
+	}
+	if filter.LotName != "" {
+		query = query.Where("lot_name = ?", filter.LotName)
+	}
+
+	query.Count(&total)
+
+	err := query.
+		Order("FIELD(severity, 'critical', 'high', 'medium', 'low')").
+		Order("created_at DESC").
+		Offset(offset).
+		Limit(limit).
+		Find(&alerts).Error
+
+	return alerts, total, err
+}
+
+func (r *AlertRepository) CountByStatus(status models.AlertStatus) (int64, error) {
+	var count int64
+	err := r.db.Model(&models.PricingAlert{}).
+		Where("status = ?", status).
+		Count(&count).Error
+	return count, err
+}
+
+func (r *AlertRepository) UpdateStatus(id uint, status models.AlertStatus) error {
+	return r.db.Model(&models.PricingAlert{}).
+		Where("id = ?", id).
+		Update("status", status).Error
+}
+
+func (r *AlertRepository) ExistsByLotAndType(lotName string, alertType models.AlertType) (bool, error) {
+	var count int64
+	err := r.db.Model(&models.PricingAlert{}).
+		Where("lot_name = ? AND alert_type = ? AND status IN ('new', 'acknowledged')", lotName, alertType).
+		Count(&count).Error
+	return count > 0, err
+}