refactor(server): decouple services and improve architecture

- Introduce interfaces for all major services (JWT, PostAI, Comment, Message, Notification, QRCodeLogin, Upload, Vote, etc.) to support dependency inversion.
- Move query parameters from `internal/dto` to a new `internal/query` package to separate request payloads from data transfer objects.
- Refactor `internal/router` to use embedded `RouterDeps` for cleaner dependency management.
- Decouple handlers from repositories by injecting services instead of direct repository access, ensuring proper layering.
- Improve database initialization by moving it from `internal/model` to `internal/database`.
- Optimize message decryption by implementing a more efficient `BatchDecrypt` method in `MessageEncryptor` using a worker pool.
- Enhance error handling and security by implementing fail-fast checks for encryption key length during startup.
- Clean up unused code, including the `avatar` package and several unused DTOs.

internal/service/group_service.go

@@ -47,7 +47,6 @@ var (
 	ErrGroupRequestHandled  = apperrors.ErrGroupRequestHandled
 	ErrNotRequestTarget     = apperrors.ErrNotRequestTarget
 	ErrNoEligibleInvitee    = apperrors.ErrNoEligibleInvitee
-	ErrNotMutualFollow      = apperrors.ErrNotMutualFollow
 	ErrInviteNotAccepted    = apperrors.ErrInviteNotAccepted
 )