feat: add projects flow and consolidate default project handling

internal/models/configuration.go

@@ -44,6 +44,7 @@ type Configuration struct {
 	UUID           string      `gorm:"size:36;uniqueIndex;not null" json:"uuid"`
 	UserID         *uint       `json:"user_id,omitempty"` // Legacy field, no longer required for ownership
 	OwnerUsername  string      `gorm:"size:100;not null;default:'';index" json:"owner_username"`
+	ProjectUUID    *string     `gorm:"size:36;index" json:"project_uuid,omitempty"`
 	AppVersion     string      `gorm:"size:64" json:"app_version,omitempty"`
 	Name           string      `gorm:"size:200;not null" json:"name"`
 	Items          ConfigItems `gorm:"type:json;not null" json:"items"`