Init world. Basic registry API server

Work in progress .
This commit adds the core registry service implementation with methods to:
- Retrieve all registry entries
- List entries with cursor-based pagination
- Fetch specific server details by ID

internal/service/service.go

@@ -0,0 +1,9 @@
+package service
+
+import "github.com/modelcontextprotocol/registry/internal/model"
+
+// RegistryService defines the interface for registry operations
+type RegistryService interface {
+	List(cursor string, limit int) ([]model.Entry, string, error)
+	GetByID(id string) (*model.ServerDetail, error)
+}