Services: delete dead RelationshipService; rename persistence to snippet-persistence

docs/architecture/01-state-and-stores.md

@@ -398,7 +398,7 @@ every keystroke. A startup subscriber observes the draft and debounces the expen
 work:
 
 ```ts
-// src/app/orchestration/persistence.ts
+// src/app/orchestration/snippet-persistence.ts
 import { useSnippetStore } from '../stores/SnippetStore';
 import { saveSnippet } from '../infrastructure/snippet-store'; // IndexedDB adapter