plugins: add Session 0.2.2 - #72

What is this?

Session, a bar widget: Session menu on the QS Bar: shut down, reboot, hibernate, or lock via ryoku-shell.

Checklist

• One folder under its catalogue with a manifest and a real preview image (not a placeholder).
• One entry added to that catalogue's registry.json (lastUpdated in YYYY-MM-DD; official: false for community items).
• Tested live in Ryoku, it renders and behaves correctly (installed with ryoku plugin add).
• tests/validate-catalogue.sh passes from the repo root.
• I own or have permission to submit this content, and it is licensed for redistribution.
• It does not overwrite user configuration or run privileged commands without clear consent.

Opened with ryoku plugin share; the product manifest and the registry entry were generated from the installed plugin.