Add unit tests for dataset, revision and task services (#686)

Brings the three under-covered services up to the testing-initiative
target:

- dataset.ts:  50% -> 99.6% statements
- revision.ts: 31% -> 93.5% statements
- task.ts:     14% -> 100% statements

Covers happy and unhappy paths across each service's public methods,
including task lifecycle and status transitions, revision draft/approval
flows and dataset fact-table replacement.

dataset.ts: drop the dead revisionIndex === 1 guard around the
dimension/measure reset (the surrounding code already guarantees only
the first revision reaches it) and use the injected this.fileService
instead of getFileService() so the draft-revision delete path is
unit-testable.

Raise the global coverage thresholds in jest.config.ts to match the new
floor (statements 79, branches 67, functions 75, lines 79).

Author: wheelsandcogs

jest.config.ts

@@ -25,10 +25,10 @@ const config: Config = {
   coverageReporters: ['cobertura', 'lcov', 'html', 'text'],
   coverageThreshold: {
     global: {
-      statements: 61,
-      branches: 49,
-      functions: 57,
-      lines: 61
+      statements: 79,
+      branches: 67,
+      functions: 75,
+      lines: 79
     }
   },
   projects: [

src/services/dataset.ts

@@ -45,7 +45,6 @@ import {
 import { StorageService } from '../interfaces/storage-service';
 import { TempFile } from '../interfaces/temp-file';
 import { dbManager } from '../db/database-manager';
-import { getFileService } from '../utils/get-file-service';
 import { bootstrapCubeBuildProcess } from '../utils/lookup-table-utils';
 
 export class DatasetService {
@@ -118,10 +117,9 @@ export class DatasetService {
       col.factTableColumn = col.columnName;
     });
 
-    if (draftRevision.revisionIndex === 1) {
-      await removeAllDimensions(dataset);
-      await removeMeasure(dataset);
-    }
+    // only the first revision can have its fact table replaced (guarded above), so always reset its dimensions/measure
+    await removeAllDimensions(dataset);
+    await removeMeasure(dataset);
 
     await RevisionRepository.replaceDataTable(draftRevision, dataTable);
     await DatasetRepository.replaceFactTable(dataset, dataTable);
@@ -356,13 +354,12 @@ export class DatasetService {
     }
 
     const cubeDB = dbManager.getCubeDataSource().createQueryRunner();
-    const fileService = getFileService();
     try {
       logger.warn(`Deleting draft revision ${revisionId} from cube database and data lake...`);
       await cubeDB.query(pgformat('DROP SCHEMA IF EXISTS %I CASCADE', revisionId));
       if (draft.dataTable?.id) {
         await cubeDB.query(pgformat('DROP TABLE IF EXISTS data_tables.%I;', draft.dataTable?.id));
-        await fileService.delete(draft.dataTable.id, datasetId);
+        await this.fileService.delete(draft.dataTable.id, datasetId);
       }
     } catch (err) {
       logger.warn(