Add stale issue workflow

[cristianrgreco]

Summary of changes

• add a new GitHub Actions workflow to mark stale issues and close inactive issues (actions/stale@v10)
• configure stale timing to 90 days and close timing to 30 days
• disable stale/close handling for pull requests in that workflow
• pin workflow runners to ubuntu-22.04 in both stale-issues and dependency-review workflows

Verification commands run

• npm run format
• npm run lint

Test results summary

• format: pass
• lint: pass
• targeted tests: not run (workflow/docs changes only)

Non-breaking evidence

• changes are limited to repository automation/workflow config and contributor process documentation
• no runtime source code or public API changes

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