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/models/configuration.go

@@ -63,6 +63,7 @@ type Configuration struct {
 	OnlyInStock           bool        `gorm:"default:false" json:"only_in_stock"`
 	PriceUpdatedAt        *time.Time  `gorm:"type:timestamp" json:"price_updated_at,omitempty"`
 	CreatedAt             time.Time   `gorm:"autoCreateTime" json:"created_at"`
+	CurrentVersionNo      int         `gorm:"-" json:"current_version_no,omitempty"`
 
 	User *User `gorm:"foreignKey:UserID" json:"user,omitempty"`
 }