Migrate mkjs to Bun-first ES6/TypeScript entrypoints and modernize multiplayer server

[Qainguin]

Motivation

• Modernize the legacy ES5 inline runtime so the app can be developed and served with a modern toolchain (Bun) and ES module loading semantics.
• Convert server runtime to TypeScript ES modules for better type-safety and to run the dedicated multiplayer server with Bun.
• Preserve the original runtime ordering and behavior so existing legacy engine scripts continue to work without a large rewrite.

Description

• Replaced the large inline script boot in index.html with a single ES module entry code/bootstrap.ts that dynamically injects the legacy script files in the original order and ported the bootstrap/game-loop to TypeScript.
• Added Bun + TypeScript project scaffolding: package.json, tsconfig.json, and bun.lock with convenient scripts (dev, serve, server, typecheck).
• Migrated the dedicated server into TypeScript ES modules in server/server.ts and server/modules/mkjsInstance.ts, added Bun run scripts (server/run.sh, server/run.bat), and kept small deprecation shims (server/server.js, server/modules/mkjsInstance.js) to avoid breaking existing workflows.
• Small runtime/type fixes made during migration (for example using ArrayBufferLike for packet buffers) and preserved the existing binary relay behavior for multiplayer packets.

Testing

• Ran bun install to populate dependencies and bun run typecheck (TypeScript) which passed after a small type adjustment to server/modules/mkjsInstance.ts.
• Started the server with bun run server --help which boots and reports the listening address, indicating the WebSocket server starts correctly.
• Executed an in-process simulation via bun -e that created a MkjsInstance with two mock clients and sent a binary kart packet, which verified the server-side binary relay path (succeeded).
• Launched the Bun HTML dev server via bun index.html which served the new index.html entrypoint successfully (dev server started), but an automated Playwright attempt to capture a screenshot failed due to a Chromium crash in the execution environment (not a project failure).

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Codex Task