refactor: move gateway and vault packages to internal directory

internal/vault/handlers/authorization_handler.go

@@ -0,0 +1,23 @@
+package handlers
+
+import (
+	"github.com/labstack/echo/v4"
+)
+
+func GrantAuthorization(e echo.Context) error {
+	// Implement authorization endpoint using passkey authentication
+	// Store session data in cache
+	return nil
+}
+
+func GetJWKS(e echo.Context) error {
+	// Implement token endpoint
+	// Use cached session data for validation
+	return nil
+}
+
+func GetToken(e echo.Context) error {
+	// Implement token endpoint
+	// Use cached session data for validation
+	return nil
+}