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>

waybar/config.jsonc

@@ -5,14 +5,7 @@
 
   "modules-left": ["niri/workspaces"],
   "modules-center": ["custom/clock"],
-  "modules-right": ["cpu", "temperature", "custom/power-profile", "custom/fan-profile", "pulseaudio", "network", "battery", "custom/mouse-battery", "group/tray-drawer"],
-  "custom/mouse-battery": {
-    "exec": "~/.config/waybar/mouse-battery.sh",
-    "interval": 60,
-    "format": " {output}",
-    "tooltip": false
-  },
-
+  "modules-right": ["cpu", "temperature", "custom/power-profile", "custom/fan-profile", "pulseaudio", "network", "battery", "tray"],
   "cpu": {
     "format": "  {usage}%",
     "format-tooltip": "{usage}% total\n{icon0} {icon1} {icon2} {icon3}\n{icon4} {icon5} {icon6} {icon7}\n{icon8} {icon9} {icon10} {icon11}",
@@ -73,21 +66,6 @@
     "spacing": 8
   },
 
-  "group/tray-drawer": {
-    "orientation": "horizontal",
-    "drawer": {
-      "transition-duration": 200,
-      "transition-left-to-right": true,
-      "click-to-reveal": true
-    },
-    "modules": ["custom/tray-arrow", "tray"]
-  },
-
-  "custom/tray-arrow": {
-    "format": "",
-    "tooltip": false
-  },
-
   "network": {
     "format-wifi": "  {essid}",
     "format-ethernet": "󰈀",