fix: add nolint:errcheck comments for intentionally unchecked errors

Add //nolint:errcheck comments to intentionally unchecked error returns:

- defer X.Close() calls: errors from closing read-only resources, rows
  after iteration, files, response bodies, and gzip readers are not
  actionable and don't affect correctness

- defer tx.Rollback(): standard Go pattern where rollback after
  successful commit returns an error, which is expected behavior

- defer stmt.Close(): statements are closed with their transactions

- Cleanup operations: DeleteRevision on failure and os.RemoveAll for
  temp directories are best-effort cleanup

- HTTP response encoding: if JSON encoding fails at response time,
  there's nothing useful we can do

- Test/benchmark code: unchecked errors in test setup/cleanup where
  failures will surface through test assertions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/mcp/transport_http.go

@@ -182,6 +182,7 @@ func (t *HTTPTransport) handlePost(w http.ResponseWriter, r *http.Request) {
 	if err := json.Unmarshal(body, &req); err != nil {
 		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(http.StatusOK)
+		//nolint:errcheck // response already being written, can't handle encode error
 		json.NewEncoder(w).Encode(Response{
 			JSONRPC: "2.0",
 			Error: &Error{
@@ -237,7 +238,7 @@ func (t *HTTPTransport) handlePost(w http.ResponseWriter, r *http.Request) {
 
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusOK)
-	json.NewEncoder(w).Encode(resp)
+	_ = json.NewEncoder(w).Encode(resp) //nolint:errcheck // response already being written
 }
 
 // handleInitialize handles the initialize request and creates a new session.
@@ -271,7 +272,7 @@ func (t *HTTPTransport) handleInitialize(w http.ResponseWriter, r *http.Request,
 	w.Header().Set("Content-Type", "application/json")
 	w.Header().Set("Mcp-Session-Id", session.ID)
 	w.WriteHeader(http.StatusOK)
-	json.NewEncoder(w).Encode(resp)
+	_ = json.NewEncoder(w).Encode(resp) //nolint:errcheck // response already being written
 }
 
 // handleGet handles SSE stream for server-initiated notifications.