refactor(layout): relocate go.mod to backend/ and clean import paths to module root

- Relocated go.mod and go.sum into backend/ root directory
- Stripped redundant backend/ segments from all Go imports (github.com/Rain-kl/Wavelet/...)
- Unified Makefile, swagger, and build-test to execute in backend/ module context
- Ensured 100% build-test, code-check, format, and swagger pass

backend/plugins/domain/cap/handlers.go

@@ -6,9 +6,9 @@ package cap
 import (
 	"net/http"
 
-	"github.com/Rain-kl/Wavelet/backend/pkg/logger"
-	"github.com/Rain-kl/Wavelet/backend/pkg/response"
-	"github.com/Rain-kl/Wavelet/backend/plugins/domain/cap/pow"
+	"github.com/Rain-kl/Wavelet/pkg/logger"
+	"github.com/Rain-kl/Wavelet/pkg/response"
+	"github.com/Rain-kl/Wavelet/plugins/domain/cap/pow"
 	"github.com/gin-gonic/gin"
 )
 

backend/plugins/domain/cap/manager.go

@@ -13,9 +13,9 @@ import (
 	"sync"
 	"time"
 
-	"github.com/Rain-kl/Wavelet/backend/pkg/config"
-	"github.com/Rain-kl/Wavelet/backend/plugins/domain/cap/pow"
-	db "github.com/Rain-kl/Wavelet/backend/plugins/infra/cache"
+	"github.com/Rain-kl/Wavelet/pkg/config"
+	"github.com/Rain-kl/Wavelet/plugins/domain/cap/pow"
+	db "github.com/Rain-kl/Wavelet/plugins/infra/cache"
 )
 
 const (

backend/plugins/domain/cap/middleware.go

@@ -6,7 +6,7 @@ package cap
 import (
 	"github.com/gin-gonic/gin"
 
-	"github.com/Rain-kl/Wavelet/backend/pkg/response"
+	"github.com/Rain-kl/Wavelet/pkg/response"
 )
 
 // VerifyMiddleware returns a Gin middleware that checks and consumes the X-Cap-Token header.

backend/plugins/domain/cap/plugin.go

@@ -5,8 +5,8 @@
 package cap
 
 import (
-	"github.com/Rain-kl/Wavelet/backend/core"
-	"github.com/Rain-kl/Wavelet/backend/core/extpoints"
+	"github.com/Rain-kl/Wavelet/core"
+	"github.com/Rain-kl/Wavelet/core/extpoints"
 )
 
 // Plugin implements core.Plugin to provide CAPTCHA generation, validation, and route protection.

backend/plugins/domain/cap/runtime_settings.go

@@ -14,9 +14,9 @@ import (
 
 	"golang.org/x/sync/singleflight"
 
-	"github.com/Rain-kl/Wavelet/backend/pkg/util"
-	cachepkg "github.com/Rain-kl/Wavelet/backend/plugins/infra/cache"
-	database "github.com/Rain-kl/Wavelet/backend/plugins/infra/database"
+	"github.com/Rain-kl/Wavelet/pkg/util"
+	cachepkg "github.com/Rain-kl/Wavelet/plugins/infra/cache"
+	database "github.com/Rain-kl/Wavelet/plugins/infra/database"
 )
 
 const (