refactor: enforce Controller → Service → Repository layering throughout backend
- Created TagService: encapsulates all tag find/create/update/delete operations
- Extended PersonService: added findAll(), getById(), getAllById(), findOrCreateByAlias()
- Extended UserService: added createGroup(), updateGroup(), deleteGroup(), getGroupById()
- DocumentService: replaced direct PersonRepository/TagRepository access with
PersonService/TagService calls; added getDocumentById(), getDocumentsBySender(),
getConversationFiltered(), deleteTagCascading()
- MassImportService: replaced PersonRepository/TagRepository with PersonService/TagService
- PersonController: removed direct repo injections, delegates to PersonService/DocumentService
- DocumentController: removed DocumentRepository injection, delegates to DocumentService
- TagController: removed TagRepository/DocumentRepository, delegates to TagService/DocumentService
- GroupController: removed UserGroupRepository injection, delegates to UserService
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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