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

pkg/persistence/errs.go

@@ -0,0 +1,12 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package db
+
+const (
+	errRedisHashSetFailed    = "failed to set redis hash: %w"
+	errRedisHashDeleteFailed = "failed to delete redis hash field: %w"
+	errUnmarshalDataFailed   = "failed to unmarshal data: %w"
+	errMarshalDataFailed     = "failed to marshal data: %w"
+	errRedisKeySetFailed     = "failed to set redis key: %w"
+)