fix: use tag-specific complexity reports (#857)

* fix(expand-task): Use tag-specific complexity reports

- Add getTagAwareFilePath utility function to resolve tag-specific file paths
- Update expandTask to use tag-aware complexity report paths
- Fix issue where expand-task always used default complexity report
- Add comprehensive tests for getTagAwareFilePath utility
- Ensure proper handling of file extensions and directory structures

Fixes #850: Expanding tasks not using tag-specific complexity reports

The expandTask function now correctly uses complexity reports specific
to the current tag context (e.g., task-complexity-report_feature-branch.json)
instead of always using the default task-complexity-report.json file.

This enables proper task expansion behavior when working with multiple
tag contexts, ensuring complexity analysis is tag-specific and accurate.

* chore: Add changeset for tag-specific complexity reports fix

* test(expand-task): Add tests for tag-specific complexity report integration

- Introduced a new test suite for verifying the integration of tag-specific complexity reports in the expandTask function.
- Added a test case to ensure the correct complexity report is used when available for a specific tag.
- Mocked file system interactions to simulate the presence of tag-specific complexity reports.

This enhances the test coverage for task expansion behavior, ensuring it accurately reflects the complexity analysis based on the current tag context.

* refactor(task-manager): unify and simplify tag-aware file path logic and tests

- Reformatted imports and cleaned up comments in test files for readability
- Centralized mocks: moved getTagAwareFilePath & slugifyTagForFilePath
  mocks to setup.js for consistency and maintainability
- Simplified utils/getTagAwareFilePath: replaced manual parsing with
  path.parse() & path.format(); improved extension handling
- Enhanced test mocks for path.parse, path.format & reset path.join
  in beforeEach to avoid interference
- All tests now pass consistently; no change in functionality

tests/unit/scripts/modules/task-manager/analyze-task-complexity.test.js

@@ -2,6 +2,10 @@
  * Tests for the analyze-task-complexity.js module
  */
 import { jest } from '@jest/globals';
+import {
+	createGetTagAwareFilePathMock,
+	createSlugifyTagForFilePathMock
+} from './setup.js';
 
 // Mock the dependencies before importing the module under test
 jest.unstable_mockModule('../../../../../scripts/modules/utils.js', () => ({
@@ -32,6 +36,8 @@ jest.unstable_mockModule('../../../../../scripts/modules/utils.js', () => ({
 	ensureTagMetadata: jest.fn((tagObj) => tagObj),
 	getCurrentTag: jest.fn(() => 'master'),
 	flattenTasksWithSubtasks: jest.fn((tasks) => tasks),
+	getTagAwareFilePath: createGetTagAwareFilePathMock(),
+	slugifyTagForFilePath: createSlugifyTagForFilePathMock(),
 	markMigrationForNotice: jest.fn(),
 	performCompleteTagMigration: jest.fn(),
 	setTasksForTag: jest.fn(),