Theme-toggle button now paints a Sun glyph in dark mode (click → light) and a Moon glyph in light mode (click → dark); the Sun icon was hardcoded before. Adds Icon::Moon (lucide crescent) and threads theme_mode into TopBar.
Bumps the casement submodule with a fix for the native macOS traffic-light reposition: idempotent absolute placement against resize, baseline invalidation on fullscreen exit, and a poison guard so a transitional re-capture can't drop the lights below their default position.
2efca5aa3b