refactor(layout): consolidate backend codebase into backend/ package and clean root directory

- Moved cmd/, core/, plugins/, pkg/, downstream/, and main.go into backend/ directory
- Batch updated all Go source files to import github.com/Rain-kl/Wavelet/backend/...
- Updated Makefile, scripts/swagger.sh, architecture guards, and platform skills
- Passed all quality gates (100% tests, 0 lint issues, clean build)

backend/cmd/app_test.go

@@ -0,0 +1,82 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package cmd
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/Rain-kl/Wavelet/backend/core"
+)
+
+func TestNewWaveletAppProfiles(t *testing.T) {
+	profiles := []core.Profile{
+		core.ProfileAPI,
+		core.ProfileWorker,
+		core.ProfileSchedule,
+		core.ProfileAll,
+	}
+
+	for _, prof := range profiles {
+		t.Run(string(prof), func(t *testing.T) {
+			app := newWaveletApp(prof)
+			require.NotNil(t, app)
+			assert.Equal(t, prof, app.Profile())
+
+			// Verify 4 infra plugins + 8 domain plugins + 3 driver plugins registered
+			plugins := app.Plugins()
+			assert.Len(t, plugins, 15)
+
+			// Verify each standard infra plugin is registered
+			_, ok := app.Plugin("database")
+			assert.True(t, ok, "database plugin missing")
+
+			_, ok = app.Plugin("cache")
+			assert.True(t, ok, "cache plugin missing")
+
+			_, ok = app.Plugin("logger")
+			assert.True(t, ok, "logger plugin missing")
+
+			_, ok = app.Plugin("storage")
+			assert.True(t, ok, "storage plugin missing")
+
+			// Verify domain plugins
+			_, ok = app.Plugin("auth")
+			assert.True(t, ok, "auth plugin missing")
+
+			_, ok = app.Plugin("user")
+			assert.True(t, ok, "user plugin missing")
+
+			_, ok = app.Plugin("message_gateway")
+			assert.True(t, ok, "message_gateway plugin missing")
+
+			_, ok = app.Plugin("risk_control")
+			assert.True(t, ok, "risk_control plugin missing")
+
+			_, ok = app.Plugin("admin")
+			assert.True(t, ok, "admin plugin missing")
+
+			_, ok = app.Plugin("upload")
+			assert.True(t, ok, "upload plugin missing")
+
+			_, ok = app.Plugin("cap")
+			assert.True(t, ok, "cap plugin missing")
+
+			_, ok = app.Plugin("system")
+			assert.True(t, ok, "system plugin missing")
+
+			// Verify driver plugins
+			_, ok = app.Plugin("driver_http")
+			assert.True(t, ok, "http driver missing")
+
+			_, ok = app.Plugin("driver_asynq_worker")
+			assert.True(t, ok, "worker driver missing")
+
+			_, ok = app.Plugin("driver_asynq_cron")
+			assert.True(t, ok, "scheduler driver missing")
+		})
+	}
+}