Description

This PR changes the default attachmentsDir from .vitest-attachments to .vitest/attachments to follow the new convention established in #9952, where all Vitest output should be organized under the .vitest/ directory.

Changes:

• Updated default attachmentsDir from .vitest-attachments to .vitest/attachments
• Updated .gitignore to ignore .vitest (covers all subdirectories including /attachments)
• Updated documentation examples to upload .vitest/** in GitHub Actions workflows
• Updated all test snapshots to reflect the new path structure

Resolves #10183

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.
• Please check Allow edits by maintainers to make review process faster. Note that this option is not available for repositories that are owned by Github organizations.

Tests

• Run the tests with pnpm test:ci.
• Updated test snapshots in test/cli/test/annotations.test.ts and test/cli/test/artifacts.test.ts
• All 22 tests passing (annotations + artifacts)

Documentation

• Updated docs/config/attachmentsdir.md with new default value
• Updated docs/guide/improving-performance.md with simplified GitHub Actions examples
• Updated docs/guide/browser/visual-regression-testing.md with new path examples
• Regenerated docs/guide/cli-generated.md

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.