revert tray drawer feature and remove mouse-battery module

The tray drawer added complexity (drawer config, custom chevron module,
state-feedback CSS) for what amounts to a small visual refinement.
Removed in favour of the original always-visible tray. The mouse-battery
indicator was also removed from the bar.

Deletes:
- waybar/mouse-battery.sh + symlink + install.sh entry
- group/tray-drawer + custom/mouse-battery blocks in config.jsonc
- #custom-tray-arrow rules from style.css
- docs/superpowers/{specs,plans} for the drawer feature

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

install.sh

@@ -25,7 +25,6 @@ ln -sf "$(pwd)/networkmanager-dmenu/config.ini" ~/.config/networkmanager-dmenu/c
 ln -sf "$(pwd)/niri/config.kdl" ~/.config/niri/config.kdl
 ln -sf "$(pwd)/waybar/config.jsonc" ~/.config/waybar/config.jsonc
 ln -sf "$(pwd)/waybar/style.css" ~/.config/waybar/style.css
-ln -sf "$(pwd)/waybar/mouse-battery.sh" ~/.config/waybar/mouse-battery.sh
 mkdir -p ~/.config/theme
 ln -sf "$(pwd)/theme/colors.css" ~/.config/theme/colors.css
 ln -sf "$(pwd)/wofi/config" ~/.config/wofi/config