refactor: replace Bun APIs with Node.js equivalents

Replace Bun.argv with process.argv, Bun.file() with fs/promises,
Bun.stringWidth with string-width package, and Bun.wrapAnsi with
wrap-ansi package for better compatibility.

index.ts

@@ -7,7 +7,7 @@ import { Conversation } from "./src/conversation";
 import Renderer from "./src/render";
 
 const { values: args, positionals } = parseArgs({
-  args: Bun.argv,
+  args: process.argv,
   options: {
     model: { type: "string" },
     m: { type: "string" },