Add source_site_id to ActiveSite model and implement unique constraint. Update serializers and views for site registration and claiming. Enhance tests for site registration and claiming functionality.

types/api.ts

@@ -43,6 +43,7 @@ export type ActiveSite = {
   id: number;
   code: string;
   name: string;
+  source_site_id: string;
   api_base_url: string;
   has_api_key: boolean;
   managed_by?: number | null;
@@ -57,7 +58,7 @@ export type ActiveSite = {
 
 export type ActiveSiteWrite = {
   code: string;
-  name: string;
+  name?: string;
   api_base_url?: string;
   api_key?: string;
   is_active?: boolean;