mock.module("fs/promises") on Linux Bun poisons the entire mock
tracking system — not just fs mocks, but ALL mock/spy assertions
(octokit mocks, spyOn(global, "fetch"), etc.) stop recording calls.
Replace with dependency injection: downloadCommentImages() now accepts
an optional fsDeps parameter. Tests pass mock mkdir/writeFile directly.
Production callers omit it and get real fs. No mock.module anywhere.
Fixes 18 test failures blocking CI on Forgejo Linux runners.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>