feat: browser UI distribution (hosted app or DevTools panel)

[jamilagibson]

Context

The browser UI currently runs as a local Vite dev server at localhost:5173. For real distribution it needs a stable, accessible entry point for developers.

Options

1. Hosted web app — simplest; users navigate to a URL; no install required
2. Chrome/Firefox DevTools panel — most professional; integrates into existing DevTools workflow (tracked separately as a v1.0.0 item)
3. Bundled Electron app — standalone desktop app; higher packaging complexity

Acceptance criteria

• Browser UI accessible via a stable URL or install mechanism (not localhost:5173)
• UI connects to the WebSocket server using the agreed server distribution strategy
• Works in Chrome and Firefox