test: fix autocomplete test to match API response structure

- Update test to unmarshal response object before extracting results array
- API returns {"results": [...], "total": N}, not a bare array
- Fixes "cannot unmarshal object into Go value of type []map" error
- Test now correctly handles the structured autocomplete response

The handleFieldValuesSearch endpoint returns a structured response
with metadata (results array + total count), not a bare array.
This aligns the test with the actual API response format.

cmd/server/tests/tags_filter_test.go

@@ -110,9 +110,11 @@ func TestTagsFilter(t *testing.T) {
 
 		assert.Equal(t, http.StatusOK, rec.Code, "Should return autocomplete results")
 
-		var results []map[string]interface{}
-		err := json.Unmarshal(rec.Body.Bytes(), &results)
+		var response map[string]interface{}
+		err := json.Unmarshal(rec.Body.Bytes(), &response)
 		require.NoError(t, err)
+
+		results := response["results"].([]map[string]interface{})
 		assert.Greater(t, len(results), 0, "Should return 'Science Fiction' in autocomplete results")
 	})