Add @opentui/web package for browser rendering

[remorses]

Adds a new @opentui/web package that enables rendering opentui apps in the browser via WebSocket.

Changes:

• New @opentui/core span capture API (getSpanLines, captureSpans)
• WebSocket server that streams terminal frames to browser clients
• HTML renderer that applies span styling (colors, bold, italic, etc.)
• Proper mouse event handling (down/up/scroll)
• Keyboard input forwarding

Usage:

import { opentuiWebSocket } from "@opentui/web"

const ws = opentuiWebSocket({
  onConnection: (session) => {
    const root = createRoot(session.renderer)
    root.render(<App />)
    return () => root.unmount()
  },
})

Bun.serve({ fetch: ws.fetch, websocket: ws.websocket })