feat(bot): implement category selection flow and commands

Author: Akinator31

crates/rustmail/src/bot.rs

@@ -147,6 +147,7 @@ pub async fn run_bot(
     registry.register_command(PingCommand);
     registry.register_command(SnippetCommand);
     registry.register_command(StatusCommand);
+    registry.register_command(CategoryCommand);
 
     let registry = Arc::new(registry);
 

crates/rustmail/src/commands/category/mod.rs

@@ -0,0 +1,5 @@
+pub mod slash_command;
+pub mod text_command;
+
+pub use slash_command::*;
+pub use text_command::*;