feat: scaffold codespace backend

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/model/workspace.go

@@ -0,0 +1,11 @@
+package model
+
+// CreateWorkspaceRequest is the request body for creating a workspace.
+type CreateWorkspaceRequest struct {
+	ID string `json:"id"`
+}
+
+// WorkspaceResponse is the API response for a workspace.
+type WorkspaceResponse struct {
+	ID string `json:"id"`
+}