modularise chat commands and add error handling for wrong commands

devdocs/CHAT-COMMANDS.md

@@ -0,0 +1,25 @@
+# Chat Commands
+
+Chat commands are modular and located in `public/js/chat-commands/`.
+
+## Adding a Command
+
+1. Create `chat-commands/mycommand.js`:
+```javascript
+export const myCommand = {
+  description: "What it does",
+  execute: () => {
+    const output = document.getElementById("terminal-output");
+    // implementation
+  },
+};
+```
+
+2. Import and register in `commands.js`:
+```javascript
+import { myCommand } from "./chat-commands/mycommand.js";
+
+const actions = {
+  // ... existing commands
+  "/mycommand": myCommand,
+};