Add the Discord community to the Learn menu

Every other pointer at the community lives in an error path or a doc, so
there was no way to reach it from the menu. Prefer the Discord app when
it is installed, and fall back to the invite in a browser when it is not.

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

default/omarchy/omarchy-menu.jsonc

@@ -45,6 +45,7 @@
   "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"},
+  "learn.community": {"icon":"󰙯","label":"Community","action":"omarchy-launch-discord-community"},
 
   // Trigger
   "trigger.emoji": {"icon":"","label":"Emoji","aliases":["emoji","emojis"],"action":"omarchy-menu-emoji"},