Add sunset-based night light scheduling

[gaburn]

Summary

• add timezone-aware sunrise and sunset scheduling for Night Light
• add a fixed-position Night Light indicator with a right-click mode panel
• keep manual controls, timezone refreshes, CLI status, menu entries, and documentation in sync
• cover solar calculations, schedule persistence, fixed indicator placement, and panel interactions

Tests

• ./test/cli
• bash test/shell.d/qml-text-format-test.sh
• bash test/shell.d/indicator-contract-test.sh
• bash test/shell.d/nightlight-test.sh
• bash test/shell.d/timezone-test.sh

The aggregate shell suite also ran; its remaining failures require the unavailable sibling omarchy-pkgs checkout (config-test.sh, snapper-test.sh, and unowned-system-paths-test.sh).

Screenshot

[cmdrrobin]

This would be a nice addition to Omarchy