Large refactor that renames/moves core types into a new Govor.Domain surface and reorganizes the Application layer. Models, configurations, migrations and many files moved from Govor.Core/Govor.Data to Govor.Domain; numerous Application services, interfaces and implementations were relocated or added (authentication, friends, messages, medias, push notifications, user sessions, storage, synching, private chats, etc.). Tests updated to use Govor.Domain namespaces and adjusted project references (removed Govor.Data reference from API tests). Also updated API, Hub and mapping code and project files to reflect the new structure and naming. This is primarily a codebase-wide namespace and module reorganization to establish a Domain project and restructure application services.
Split IFriendRequestService into command and query interfaces, refactor related services and tests, and update dependency injection. Add HubResult response model and a SignalR HubExceptionFilter for consistent error handling. Move and update FriendsHub to use new command service and result pattern. Update username validation to allow digits after Cyrillic letters. Add new controllers and configuration for SignalR. Remove obsolete IFriendRequestService and related code.
Introduced ICurrentUserService and its implementation to centralize retrieval of the current user's ID from claims. Updated FriendsController to use this service instead of direct claim access. Registered the service and IHttpContextAccessor in DI. Added integration tests for FriendsController. Moved UsernameValidator to Infrastructure/Validators.
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