[AI assisted] MM-62927: add comprehensive whitespace validation tests for FileSettings paths (#31087)

https://mattermost.atlassian.net/browse/MM-62927

```release-note
NONE
```
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/config.go

@@ -4129,6 +4129,11 @@ func (s *FileSettings) isValid() *AppError {
 		return NewAppError("Config.IsValid", "model.config.is_valid.directory.app_error", nil, "", http.StatusBadRequest)
 	}
 
+	// Check for leading/trailing whitespace in directory path
+	if strings.TrimSpace(*s.Directory) != *s.Directory {
+		return NewAppError("Config.IsValid", "model.config.is_valid.directory_whitespace.app_error", map[string]any{"Setting": "FileSettings.Directory", "Value": *s.Directory}, "", http.StatusBadRequest)
+	}
+
 	if *s.MaxImageDecoderConcurrency < -1 || *s.MaxImageDecoderConcurrency == 0 {
 		return NewAppError("Config.IsValid", "model.config.is_valid.image_decoder_concurrency.app_error", map[string]any{"Value": *s.MaxImageDecoderConcurrency}, "", http.StatusBadRequest)
 	}
@@ -4141,10 +4146,22 @@ func (s *FileSettings) isValid() *AppError {
 		return NewAppError("Config.IsValid", "model.config.is_valid.storage_class.app_error", map[string]any{"Value": *s.AmazonS3StorageClass}, "", http.StatusBadRequest)
 	}
 
+	if strings.TrimSpace(*s.AmazonS3PathPrefix) != *s.AmazonS3PathPrefix {
+		return NewAppError("Config.IsValid", "model.config.is_valid.directory_whitespace.app_error", map[string]any{"Setting": "FileSettings.AmazonS3PathPrefix", "Value": *s.AmazonS3PathPrefix}, "", http.StatusBadRequest)
+	}
+
 	if *s.ExportAmazonS3StorageClass != "" && !slices.Contains([]string{StorageClassStandard, StorageClassReducedRedundancy, StorageClassStandardIA, StorageClassOnezoneIA, StorageClassIntelligentTiering, StorageClassGlacier, StorageClassDeepArchive, StorageClassOutposts, StorageClassGlacierIR, StorageClassSnow, StorageClassExpressOnezone}, *s.ExportAmazonS3StorageClass) {
 		return NewAppError("Config.IsValid", "model.config.is_valid.storage_class.app_error", map[string]any{"Value": *s.ExportAmazonS3StorageClass}, "", http.StatusBadRequest)
 	}
 
+	if strings.TrimSpace(*s.ExportAmazonS3PathPrefix) != *s.ExportAmazonS3PathPrefix {
+		return NewAppError("Config.IsValid", "model.config.is_valid.directory_whitespace.app_error", map[string]any{"Setting": "FileSettings.ExportAmazonS3PathPrefix", "Value": *s.ExportAmazonS3PathPrefix}, "", http.StatusBadRequest)
+	}
+
+	if strings.TrimSpace(*s.ExportDirectory) != *s.ExportDirectory {
+		return NewAppError("Config.IsValid", "model.config.is_valid.directory_whitespace.app_error", map[string]any{"Setting": "FileSettings.ExportDirectory", "Value": *s.ExportDirectory}, "", http.StatusBadRequest)
+	}
+
 	return nil
 }