refactor: revive cleanup — unused params to _, add missing doc comments

- admin/db_helper GetCache/GetUserService/GetAuthService: ctx -> _ (签名对称保留)
- validateMergedStorageConfig / ParseMigrationTargetConfig / MockStorageService.Put 未用参数 -> _
- SetDBServiceForTest、StorageDriver 常量组补充文档注释
lint_issues 33→26

backend/plugins/domain/admin/db_helper.go

@@ -113,22 +113,25 @@ func GetDB(ctx context.Context) *gorm.DB {
 	return dbService.DB(ctx)
 }
 
-// GetCache returns the unified CacheService instance.
-func GetCache(ctx context.Context) contracts.CacheService {
+// GetCache returns the unified CacheService instance. ctx is kept for
+// signature symmetry with the other context-aware accessors.
+func GetCache(_ context.Context) contracts.CacheService {
 	servicesMu.RLock()
 	defer servicesMu.RUnlock()
 	return cacheService
 }
 
-// GetUserService returns the UserService instance.
-func GetUserService(ctx context.Context) contracts.UserService {
+// GetUserService returns the UserService instance. ctx is kept for
+// signature symmetry with the other context-aware accessors.
+func GetUserService(_ context.Context) contracts.UserService {
 	servicesMu.RLock()
 	defer servicesMu.RUnlock()
 	return userService
 }
 
-// GetAuthService returns the AuthService instance.
-func GetAuthService(ctx context.Context) contracts.AuthService {
+// GetAuthService returns the AuthService instance. ctx is kept for
+// signature symmetry with the other context-aware accessors.
+func GetAuthService(_ context.Context) contracts.AuthService {
 	servicesMu.RLock()
 	defer servicesMu.RUnlock()
 	return authService

backend/plugins/domain/admin/handlers_config.go

@@ -507,7 +507,7 @@ func validateAndMergeStorageConfig(ctx context.Context, value, currentConfig str
 	return string(unmaskedVal), nil
 }
 
-func validateMergedStorageConfig(ctx context.Context, currentCfg, newCfg, targetCfg contracts.StorageConfigDTO) error {
+func validateMergedStorageConfig(ctx context.Context, currentCfg, newCfg, _ contracts.StorageConfigDTO) error {
 	if newCfg.Driver != "" && newCfg.Driver != currentCfg.Driver {
 		var uploadCount int64
 		gormDB := GetDB(ctx)

backend/plugins/domain/message_gateway/db_helper.go

@@ -21,6 +21,7 @@ var (
 	taskSvc  contracts.TaskService
 )
 
+// SetDBServiceForTest injects a DBService for tests. Production wiring must use Apply.
 func SetDBServiceForTest(s contracts.DBService) {
 	setDBService(s)
 }

backend/plugins/domain/upload/shared/test_helpers.go

@@ -120,7 +120,7 @@ func NewMockStorageService() *MockStorageService {
 }
 
 // Put uploads an object into mock storage.
-func (m *MockStorageService) Put(_ context.Context, key string, body io.Reader, size int64, contentType string) (contracts.StoragePutResult, error) {
+func (m *MockStorageService) Put(_ context.Context, key string, body io.Reader, _ int64, contentType string) (contracts.StoragePutResult, error) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	data, err := io.ReadAll(body)

backend/plugins/domain/upload/storage/migration.go

@@ -36,7 +36,7 @@ func LatestMigrationExecution(ctx context.Context) (*contracts.TaskExecutionDTO,
 }
 
 // ParseMigrationTargetConfig parses and validates a storage migration target payload.
-func ParseMigrationTargetConfig(ctx context.Context, payload []byte) (contracts.StorageConfigDTO, error) {
+func ParseMigrationTargetConfig(_ context.Context, payload []byte) (contracts.StorageConfigDTO, error) {
 	if strings.TrimSpace(string(payload)) == "" {
 		return contracts.StorageConfigDTO{}, errors.New("storage migration target payload is required")
 	}