docs(browser): clarify Chromium support in Browser Bridge hints

[lampten]

Description

On Linux arm64, Google Chrome is generally unavailable, so the current Chrome-only wording made it easy to assume OpenCLI does not support that environment.

I verified that the Browser Bridge works on Debian 13 arm64 with Chromium: opencli doctor connected successfully, and browser commands were able to run through the extension/daemon pipeline. In other words, the runtime already works there, but the current docs and user-facing hints can mislead Linux arm64 users into thinking Chromium is unsupported.

This PR keeps the scope narrow:

• update README.md and README.zh-CN.md to mention Chrome/Chromium explicitly
• update Browser Bridge setup, doctor, and auth/login hints to say Chrome or Chromium
• avoid behavior changes to the browser pipeline itself

Related issue:

Type of Change

• 🐛 Bug fix
• 📝 Documentation
• ✨ New feature
• 🌐 New site adapter
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Documentation (if adding/modifying an adapter)

• Added doc page under docs/adapters/ (if new adapter)
• Updated docs/adapters/index.md table (if new adapter)
• Updated sidebar in docs/.vitepress/config.mts (if new adapter)
• Updated README.md / README.zh-CN.md when command discoverability changed
• Used positional args for the command's primary subject unless a named flag is clearly better
• Normalized expected adapter failures to CliError subclasses instead of raw Error

Screenshots / Output

$ opencli doctor
opencli v1.6.1 doctor (node v22.22.1)

[OK] Daemon: running on port 19825
[OK] Extension: connected (v1.5.5)
[OK] Connectivity: connected in 0.1s

Everything looks good!

Checks run:

• npx tsc --noEmit
• npm test