fix(execution): apply timeout to non-browser commands

[Astro-Han]

Description

Non-browser commands (browser: false) ran without any timeout protection, even when the adapter explicitly set timeoutSeconds. The browser branch already wrapped execution with runWithTimeout(), but the non-browser branch called runCommand() directly.

This adds the same runWithTimeout() wrapping when a positive timeoutSeconds is configured. Also adds an optional hint to TimeoutError so non-browser timeouts show a relevant message instead of the browser-specific env var hint.

Related issue: fixes the non-browser timeout gap identified in code audit

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ 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

 PASS  src/execution.test.ts
  executeCommand — non-browser timeout
    ✓ applies timeoutSeconds to non-browser commands (13ms)
    ✓ skips timeout when timeoutSeconds is 0 (52ms)