feat: Add slashcommand api

docs-site/docs/user-guide/text-and-direct-messages.md

@@ -13,6 +13,7 @@ Text channels belong to a server. Everyone with access to that server and channe
 You can use text channels to:
 
 - send normal messages;
+- run slash commands by typing `/`;
 - edit or delete your own messages when allowed;
 - react to messages;
 - send attachments;
@@ -24,6 +25,17 @@ You can use text channels to:
 
 Direct messages are private conversations outside a server channel. Use them when a message is meant for one person instead of the server.
 
+## Slash Commands
+
+Type `/` at the start of the message box to open the slash command menu. It lists the commands you can run, with a short description for each.
+
+- Keep typing to filter the list (for example `/le`).
+- Use the up and down arrow keys to move through the list, then press `Enter` or `Tab` to pick a command. You can also click one.
+- Press `Escape` to close the menu.
+- A command that needs extra text fills the box with `/name ` so you can type the rest, then send it.
+
+MetoYou includes built-in commands such as `/lenny`, which posts `( ͡° ͜ʖ ͡°)`. Plugins can add their own commands, which appear in the same menu (tagged with the plugin name). Slash commands are available in both text channels and direct messages; some plugin commands only appear inside a server. Text that starts with `/` but matches no command is sent as a normal message.
+
 ## Attachments and Media
 
 Attachments can appear as files, images, audio, or video depending on the file type and what the app can preview. If an image or link cannot load directly, the app can use fallback paths where available.