feat: refactor tests and improve mocking for file-service and GitHub polling

- Updated mocking strategy for node:fs and node:fs/promises in file-service tests.
- Removed redundant test files and improved test implementations for better clarity.
- Enhanced GitHub polling service tests with rate limiter integration.

packages/dashboard/src/__tests__/github-poll.test.ts

@@ -118,6 +118,7 @@ describe("GitHubPollingService", () => {
       store: mockStore,
       token: "test-token",
       pollingIntervalMs: 60_000,
+      rateLimiter: new GitHubRateLimiter(),
     });
 
     mockGetBadgeStatusesBatch.mockReset();