Add configuration revisions system and project variant deletion

Features:
- Configuration versioning: immutable snapshots in local_configuration_versions
- Revisions UI: /configs/:uuid/revisions page to view version history
- Clone from version: ability to clone configuration from specific revision
- Project variant deletion: DELETE /api/projects/:uuid endpoint
- Updated CLAUDE.md with new architecture details and endpoints

Architecture updates:
- local_configuration_versions table for immutable snapshots
- Version tracking on each configuration save
- Rollback capability to previous versions
- Variant deletion with main variant protection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/services/project.go

@@ -16,9 +16,10 @@ import (
 )
 
 var (
-	ErrProjectNotFound   = errors.New("project not found")
-	ErrProjectForbidden  = errors.New("access to project forbidden")
-	ErrProjectCodeExists = errors.New("project code and variant already exist")
+	ErrProjectNotFound          = errors.New("project not found")
+	ErrProjectForbidden         = errors.New("access to project forbidden")
+	ErrProjectCodeExists        = errors.New("project code and variant already exist")
+	ErrCannotDeleteMainVariant  = errors.New("cannot delete main variant")
 )
 
 type ProjectService struct {
@@ -173,6 +174,17 @@ func (s *ProjectService) Reactivate(projectUUID, ownerUsername string) error {
 	return s.setProjectActive(projectUUID, ownerUsername, true)
 }
 
+func (s *ProjectService) DeleteVariant(projectUUID, ownerUsername string) error {
+	localProject, err := s.localDB.GetProjectByUUID(projectUUID)
+	if err != nil {
+		return ErrProjectNotFound
+	}
+	if strings.TrimSpace(localProject.Variant) == "" {
+		return ErrCannotDeleteMainVariant
+	}
+	return s.setProjectActive(projectUUID, ownerUsername, false)
+}
+
 func (s *ProjectService) setProjectActive(projectUUID, ownerUsername string, isActive bool) error {
 	return s.localDB.DB().Transaction(func(tx *gorm.DB) error {
 		var project localdb.LocalProject
@@ -263,8 +275,8 @@ func (s *ProjectService) ListConfigurations(projectUUID, ownerUsername, status s
 		}, nil
 	}
 
-	localConfigs, err := s.localDB.GetConfigurations()
-	if err != nil {
+	var localConfigs []localdb.LocalConfiguration
+	if err := s.localDB.DB().Preload("CurrentVersion").Order("created_at DESC").Find(&localConfigs).Error; err != nil {
 		return nil, err
 	}