chore: add artifact expiration policies to CI jobs

Description

chore: add artifact expiration policies to CI jobs

Add explicit artifact expiration policies to all CI jobs and reduce retention from 30 days to 7 days to optimize storage usage. Seven days provides sufficient time for MR review and debugging while reducing storage costs by approximately 75%.

Changes:

• Add 7-day expiration to lint job (code quality reports)
• Add 7-day expiration to tests:unit job (test reports)
• Reduce expiration from 30d to 7d for:
  • build_windows (Windows binaries)
  • windows_installer (installer packages)
  • snapcraft builds (snap packages)
  • signing jobs (signed artifacts)

Artifacts are only needed during MR review and short-term debugging. Release artifacts are stored separately via GitLab Releases and are not affected by pipeline artifact expiration.

Related Issues

Resolves #[issue_number]

How has this been tested?

Screenshots (if appropriate):