Add Herdr keybindings to the Learn menu

Herdr ships its own annotated keybindings menu, same as Tmux, but nothing
in the menu pointed at it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

default/omarchy/omarchy-menu.jsonc

@@ -44,6 +44,7 @@
   "learn.neovim": {"icon":"","label":"Neovim","action":"omarchy-launch-webapp 'https://www.lazyvim.org/keymaps'"},
   "learn.bash": {"icon":"󱆃","label":"Bash","action":"omarchy-launch-webapp 'https://devhints.io/bash'"},
   "learn.tmux-keybindings": {"icon":"","label":"Tmux","action":"omarchy-menu-tmux-keybindings"},
+  "learn.herdr-keybindings": {"icon":"","label":"Herdr","action":"omarchy-menu-herdr-keybindings"},
 
   // Trigger
   "trigger.emoji": {"icon":"","label":"Emoji","aliases":["emoji","emojis"],"action":"omarchy-menu-emoji"},