fix(ingestion): silence errcheck on resp.Body.Close in integration test

CI's golangci-lint flagged the un-checked deferred Close. Match the
existing project pattern (defer func() { _ = ... }()).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ingestion/internal/mcp/integration_test.go

@@ -27,7 +27,7 @@ func TestMCPMountedHandler(t *testing.T) {
 	require.NoError(t, err)
 	resp, err := http.Post(ts.URL+"/mcp", "application/json", bytes.NewReader(body))
 	require.NoError(t, err)
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	assert.Equal(t, http.StatusOK, resp.StatusCode)
 
 	out, _ := io.ReadAll(resp.Body)