Add workflow run deletion action

[ryux1]

Summary

• add an inline delete action for completed workflow runs
• require write access and a modal confirmation before deletion
• refresh both workflow run views after a successful deletion
• add coverage for the permission/status context used to expose the action

Fixes #293

Testing

• npm test -- --runInBand (34 tests)
• npm run format-check
• npm run lint
• npm run build

npm run package currently stops before compilation because vsce rejects the existing scoped package name (@github/vscode-github-actions); this change does not modify that field.