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/component.go

@@ -0,0 +1,127 @@
+package repository
+
+import (
+	"time"
+
+	"github.com/mchus/quoteforge/internal/models"
+	"gorm.io/gorm"
+)
+
+type ComponentRepository struct {
+	db *gorm.DB
+}
+
+func NewComponentRepository(db *gorm.DB) *ComponentRepository {
+	return &ComponentRepository{db: db}
+}
+
+type ComponentFilter struct {
+	Category string
+	Vendor   string
+	Search   string
+	HasPrice bool
+}
+
+func (r *ComponentRepository) List(filter ComponentFilter, offset, limit int) ([]models.LotMetadata, int64, error) {
+	var components []models.LotMetadata
+	var total int64
+
+	query := r.db.Model(&models.LotMetadata{}).
+		Preload("Lot").
+		Preload("Category")
+
+	if filter.Category != "" {
+		query = query.Joins("JOIN qt_categories ON qt_lot_metadata.category_id = qt_categories.id").
+			Where("qt_categories.code = ?", filter.Category)
+	}
+	if filter.Vendor != "" {
+		query = query.Where("vendor = ?", filter.Vendor)
+	}
+	if filter.Search != "" {
+		search := "%" + filter.Search + "%"
+		query = query.Where("lot_name LIKE ? OR model LIKE ?", search, search)
+	}
+	if filter.HasPrice {
+		query = query.Where("current_price IS NOT NULL AND current_price > 0")
+	}
+
+	query.Count(&total)
+
+	// Sort by popularity + freshness, no price goes last
+	err := query.
+		Order("CASE WHEN current_price IS NULL OR current_price = 0 THEN 1 ELSE 0 END").
+		Order("popularity_score DESC").
+		Offset(offset).
+		Limit(limit).
+		Find(&components).Error
+
+	return components, total, err
+}
+
+func (r *ComponentRepository) GetByLotName(lotName string) (*models.LotMetadata, error) {
+	var component models.LotMetadata
+	err := r.db.
+		Preload("Lot").
+		Preload("Category").
+		Where("lot_name = ?", lotName).
+		First(&component).Error
+	if err != nil {
+		return nil, err
+	}
+	return &component, nil
+}
+
+func (r *ComponentRepository) GetMultiple(lotNames []string) ([]models.LotMetadata, error) {
+	var components []models.LotMetadata
+	err := r.db.
+		Preload("Lot").
+		Preload("Category").
+		Where("lot_name IN ?", lotNames).
+		Find(&components).Error
+	return components, err
+}
+
+func (r *ComponentRepository) Update(component *models.LotMetadata) error {
+	return r.db.Save(component).Error
+}
+
+func (r *ComponentRepository) Create(component *models.LotMetadata) error {
+	return r.db.Create(component).Error
+}
+
+func (r *ComponentRepository) GetVendors(category string) ([]string, error) {
+	var vendors []string
+	query := r.db.Model(&models.LotMetadata{}).Distinct("vendor")
+	if category != "" {
+		query = query.Joins("JOIN qt_categories ON qt_lot_metadata.category_id = qt_categories.id").
+			Where("qt_categories.code = ?", category)
+	}
+	err := query.Pluck("vendor", &vendors).Error
+	return vendors, err
+}
+
+func (r *ComponentRepository) IncrementRequestCount(lotName string) error {
+	now := time.Now()
+	return r.db.Model(&models.LotMetadata{}).
+		Where("lot_name = ?", lotName).
+		Updates(map[string]interface{}{
+			"request_count":     gorm.Expr("request_count + 1"),
+			"last_request_date": now,
+		}).Error
+}
+
+// GetAllLots returns all lots from the existing lot table
+func (r *ComponentRepository) GetAllLots() ([]models.Lot, error) {
+	var lots []models.Lot
+	err := r.db.Find(&lots).Error
+	return lots, err
+}
+
+// GetLotsWithoutMetadata returns lots that don't have qt_lot_metadata entries
+func (r *ComponentRepository) GetLotsWithoutMetadata() ([]models.Lot, error) {
+	var lots []models.Lot
+	err := r.db.
+		Where("lot_name NOT IN (SELECT lot_name FROM qt_lot_metadata)").
+		Find(&lots).Error
+	return lots, err
+}