feat: Lightpanda browser support

[4ier]

What

Add Lightpanda as an alternative headless browser backend for Neo, alongside Chrome.

Lightpanda is an open-source headless browser written in Zig, purpose-built for AI agents and automation. It's 11x faster and uses 9x less memory than Chrome for headless tasks.

Changes

• neo setup auto-detects Lightpanda binary; defaults to Chrome when both available
• New browserType config field ('chrome' | 'lightpanda')
• neo start launches Lightpanda with serve --host --port when configured
• neo connect handles Lightpanda's single-WS CDP (no /json/list, uses Target.createTarget)
• Persistent WebSocket connection pool for Lightpanda (context tied to WS lifetime)
• neo open, neo read, neo snapshot, neo click all work with Lightpanda
• Always include params: {} in CDP messages (Lightpanda rejects missing params key)
• Page-load polling in context bootstrap for reliable a11y tree reads

Config

// ~/.neo/config.json
{
  "chromePath": "/usr/local/bin/lightpanda",
  "browserType": "lightpanda",  // or 'chrome' (default)
  "cdpPort": 9222
}

Tested

All core commands verified with Lightpanda nightly (bd2406f8):

Command	Status
neo connect	✅
neo open	✅
neo read	✅
neo snapshot	✅ (12 a11y nodes for example.com)
neo click	✅

Chrome remains the default and is unaffected by these changes.