refactor(bot): rename bot.hear to bot.store

Clearer what it actually does (i.e. record a message in the backlog)
and also unlocks that name for a dispatch function where we hear any
message and decide what to do with it. Currently that dispatch logic
lives inside BotAdapter in main.zig and that is not ideal.

src/main.zig

@@ -85,7 +85,7 @@ pub const BotAdapter = struct {
                     msg.targets,
                     msg.text,
                 ) catch |err| return report_error(err);
-                self.bot.hear(bot_msg);
+                self.bot.store(bot_msg);
                 return null;
             },
             .JOIN => |msg| {