[ + ] Python Package keyring

**Additions:** keyring
**Removals:** (none)

**Reason:** The PushNotification workbench (submitted at FreeCAD/Addons#133) uses `keyring` as an optional dependency to store the ntfy auth token via the OS-native credential store (macOS Keychain, Windows Credential Locker, Secret Service on Linux) instead of plaintext in FreeCAD preferences. It's a well-established, actively-maintained PyPI package with no compiled-extension requirements.

Locate the package index entry or metadata file used for Python package additions, then review nearby entries for the expected format. Add keyring as an optional dependency with the stated rationale, and verify that the index accepts the new entry.

Written by the indexing model from the issue text.