plugins: add configurable Battery Alerts to the QS Bar

[Sipper1236]

Adds Battery Alerts to the QS Bar: a native battery-alert glyph opens a compact panel with configurable warning and critical percentages, pause/resume, and a test button. Defaults are 25% and 10%. Notifications show the actual charge level, fire once per level per discharge session, and rearm on AC. A direct drop below critical emits only the critical notification.

The service reads UPower and runs only notify-send; no network, elevated privileges, or file writes. One shared monitor avoids duplicate notifications across displays. The panel uses the current host API after settings updates replace the bar slot. Ryoku Do Not Disturb suppresses popups, including critical alerts; this limitation is documented.

Validation:

• tests/validate-catalogue.sh passes with the new catalogue entry and generated product hashes.
• ryoku plugin validate reports 0 blocking findings and 0 warnings.
• Shared policy tests cover threshold crossings, rapid drops, startup below threshold, AC reset, repeated samples, disabled alerts, and invalid readings.
• Live QML harness verified repeated host setting saves, host replacement, client count, and pause/resume.
• Installed on the live QS Bar; notification delivery observed with DND off. Preview is an actual capture of the installed compact panel. The actual battery was not drained to the warning levels; threshold behavior was tested through the shared policy.

MIT licensed community contribution, maintained by rayyan (https://github.com/Sipper1236), not the Ryoku team. Submitted with the Ryoku skill using ryoku plugin share.