fix(lint): satisfy errcheck for io.Copy, json.Encode, Body.Close, deferred Close

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/mcp/server.go

@@ -80,7 +80,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(response{
+	_ = json.NewEncoder(w).Encode(response{
 		JSONRPC: "2.0",
 		ID:      req.ID,
 		Result:  result,
@@ -90,7 +90,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 func writeError(w http.ResponseWriter, id any, code int, msg string) {
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(response{
+	_ = json.NewEncoder(w).Encode(response{
 		JSONRPC: "2.0",
 		ID:      id,
 		Error:   &rpcError{Code: code, Message: msg},