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/services/configuration.go

@@ -0,0 +1,176 @@
+package services
+
+import (
+	"encoding/json"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/mchus/quoteforge/internal/models"
+	"github.com/mchus/quoteforge/internal/repository"
+)
+
+var (
+	ErrConfigNotFound   = errors.New("configuration not found")
+	ErrConfigForbidden  = errors.New("access to configuration forbidden")
+)
+
+type ConfigurationService struct {
+	configRepo    *repository.ConfigurationRepository
+	componentRepo *repository.ComponentRepository
+	quoteService  *QuoteService
+}
+
+func NewConfigurationService(
+	configRepo *repository.ConfigurationRepository,
+	componentRepo *repository.ComponentRepository,
+	quoteService *QuoteService,
+) *ConfigurationService {
+	return &ConfigurationService{
+		configRepo:    configRepo,
+		componentRepo: componentRepo,
+		quoteService:  quoteService,
+	}
+}
+
+type CreateConfigRequest struct {
+	Name       string              `json:"name"`
+	Items      models.ConfigItems  `json:"items"`
+	Notes      string              `json:"notes"`
+	IsTemplate bool                `json:"is_template"`
+}
+
+func (s *ConfigurationService) Create(userID uint, req *CreateConfigRequest) (*models.Configuration, error) {
+	total := req.Items.Total()
+
+	config := &models.Configuration{
+		UUID:       uuid.New().String(),
+		UserID:     userID,
+		Name:       req.Name,
+		Items:      req.Items,
+		TotalPrice: &total,
+		Notes:      req.Notes,
+		IsTemplate: req.IsTemplate,
+	}
+
+	if err := s.configRepo.Create(config); err != nil {
+		return nil, err
+	}
+
+	// Record usage stats
+	_ = s.quoteService.RecordUsage(req.Items)
+
+	return config, nil
+}
+
+func (s *ConfigurationService) GetByUUID(uuid string, userID uint) (*models.Configuration, error) {
+	config, err := s.configRepo.GetByUUID(uuid)
+	if err != nil {
+		return nil, ErrConfigNotFound
+	}
+
+	// Allow access if user owns config or it's a template
+	if config.UserID != userID && !config.IsTemplate {
+		return nil, ErrConfigForbidden
+	}
+
+	return config, nil
+}
+
+func (s *ConfigurationService) Update(uuid string, userID uint, req *CreateConfigRequest) (*models.Configuration, error) {
+	config, err := s.configRepo.GetByUUID(uuid)
+	if err != nil {
+		return nil, ErrConfigNotFound
+	}
+
+	if config.UserID != userID {
+		return nil, ErrConfigForbidden
+	}
+
+	total := req.Items.Total()
+
+	config.Name = req.Name
+	config.Items = req.Items
+	config.TotalPrice = &total
+	config.Notes = req.Notes
+	config.IsTemplate = req.IsTemplate
+
+	if err := s.configRepo.Update(config); err != nil {
+		return nil, err
+	}
+
+	return config, nil
+}
+
+func (s *ConfigurationService) Delete(uuid string, userID uint) error {
+	config, err := s.configRepo.GetByUUID(uuid)
+	if err != nil {
+		return ErrConfigNotFound
+	}
+
+	if config.UserID != userID {
+		return ErrConfigForbidden
+	}
+
+	return s.configRepo.Delete(config.ID)
+}
+
+func (s *ConfigurationService) ListByUser(userID uint, page, perPage int) ([]models.Configuration, int64, error) {
+	if page < 1 {
+		page = 1
+	}
+	if perPage < 1 || perPage > 100 {
+		perPage = 20
+	}
+	offset := (page - 1) * perPage
+
+	return s.configRepo.ListByUser(userID, offset, perPage)
+}
+
+func (s *ConfigurationService) ListTemplates(page, perPage int) ([]models.Configuration, int64, error) {
+	if page < 1 {
+		page = 1
+	}
+	if perPage < 1 || perPage > 100 {
+		perPage = 20
+	}
+	offset := (page - 1) * perPage
+
+	return s.configRepo.ListTemplates(offset, perPage)
+}
+
+// Export configuration as JSON
+type ConfigExport struct {
+	Name  string             `json:"name"`
+	Notes string             `json:"notes"`
+	Items models.ConfigItems `json:"items"`
+}
+
+func (s *ConfigurationService) ExportJSON(uuid string, userID uint) ([]byte, error) {
+	config, err := s.GetByUUID(uuid, userID)
+	if err != nil {
+		return nil, err
+	}
+
+	export := ConfigExport{
+		Name:  config.Name,
+		Notes: config.Notes,
+		Items: config.Items,
+	}
+
+	return json.MarshalIndent(export, "", "  ")
+}
+
+func (s *ConfigurationService) ImportJSON(userID uint, data []byte) (*models.Configuration, error) {
+	var export ConfigExport
+	if err := json.Unmarshal(data, &export); err != nil {
+		return nil, err
+	}
+
+	req := &CreateConfigRequest{
+		Name:  export.Name,
+		Notes: export.Notes,
+		Items: export.Items,
+	}
+
+	return s.Create(userID, req)
+}