fix(tests): handle all Close() and Decode() errors across integration tests

Replace all unhandled resp.Body.Close() calls throughout the test suite:

- Deferred calls: replace 'defer VAR.Body.Close()' with a closure that explicitly
  discards the error via 'defer func(Body io.ReadCloser) { _ = Body.Close() }(VAR.Body)'
- Immediate calls: replace 'VAR.Body.Close()' with '_ = VAR.Body.Close()'

Replace all unhandled json.NewDecoder(VAR.Body).Decode(&x) calls with error capture
and require.NoError assertion. Files using httptest.ResponseRecorder (collections_preview,
processing_issues) use 'err :=' declaration; suite-style tests (scanner_integration,
dashboard_integration) use s.T() instead of t.

cmd/server/tests/search_unified_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -30,7 +31,7 @@ func TestUnifiedSearch(t *testing.T) {
 	folderHTTP.Header.Set("Authorization", "Bearer "+setup.UserToken)
 	folderResp, err := client.Do(folderHTTP)
 	require.NoError(t, err)
-	folderResp.Body.Close()
+	_ = folderResp.Body.Close()
 	require.Equal(t, http.StatusCreated, folderResp.StatusCode)
 
 	// Helper to create book with fields
@@ -54,7 +55,9 @@ func TestUnifiedSearch(t *testing.T) {
 		req.Header.Set("Authorization", "Bearer "+setup.UserToken)
 		resp, err := client.Do(req)
 		require.NoError(t, err)
-		defer resp.Body.Close()
+		defer func(Body io.ReadCloser) {
+			_ = Body.Close()
+		}(resp.Body)
 		require.Equal(t, http.StatusCreated, resp.StatusCode)
 	}