fix(prettier): honor .prettierignore during checks

[davehenton]

Summary

• run the Prettier plugin from the staged repo root so Prettier discovers .prettierignore correctly
• include .gitignore in the plugin cache-affecting files to preserve Prettier's default ignore behavior
• add a regression test covering an ignored file alongside a non-ignored unformatted file

Testing

• cargo test -p qlty network_tests -- --ignored

Fixes #2499

[claude]

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[qltysh]

Coverage Impact - ubuntu-latest

This PR will not change total coverage.

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[qltysh]

Coverage Impact - macos-15

This PR will not change total coverage.

🚦 See full report on Qlty Cloud »

🛟 Help

• Diff Coverage: Coverage for added or modified lines of code (excludes deleted files). Learn more.

• Total Coverage: Coverage for the whole repository, calculated as the sum of all File Coverage. Learn more.

• File Coverage: Covered Lines divided by Covered Lines plus Missed Lines. (Excludes non-executable lines including blank lines and comments.)

  • Indirect Changes: Changes to File Coverage for files that were not modified in this PR. Learn more.