refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

core/contracts/auth.go

@@ -1,3 +1,6 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
 // Package contracts defines unified service interfaces and DTOs for cross-plugin communication.
 package contracts
 
@@ -26,6 +29,11 @@ type UserDTO struct {
 	UpdatedAt          time.Time `json:"updated_at"`
 }
 
+// TableName returns w_users.
+func (UserDTO) TableName() string {
+	return "w_users"
+}
+
 // OAuthUserInfoDTO contains user identity claims obtained from an OAuth provider.
 type OAuthUserInfoDTO struct {
 	ID                uint64 `json:"id"`