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/config/config_test.go

@@ -0,0 +1,17 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package config
+
+import "testing"
+
+func TestApplyEnvOverridesRedisMaintNotifications(t *testing.T) {
+	t.Setenv("REDIS_MAINT_NOTIFICATIONS", "true")
+
+	cfg := &configModel{}
+	applyEnvOverrides(cfg)
+
+	if !cfg.Redis.MaintNotifications {
+		t.Fatal("REDIS_MAINT_NOTIFICATIONS=true was not applied")
+	}
+}