feat: add --wait-until flag and change default to domcontentloaded

[juliobrasa]

Summary

The open command defaulted to waitUntil: 'load', which waits for all resources (analytics, third-party scripts, etc.) and frequently causes timeouts on modern SPAs.

Changes

1. Add --wait-until CLI flag — accepts load, domcontentloaded, or networkidle
2. Change default to domcontentloaded — for both handleNavigate and handleDiffUrl
3. Align with tab new — which already used domcontentloaded
4. Env var support — AGENT_BROWSER_WAIT_UNTIL

Usage

agent-browser open https://example.com                           # uses domcontentloaded
agent-browser open https://example.com --wait-until load         # wait for all resources
agent-browser open https://example.com --wait-until networkidle  # wait for network idle

Files changed

• cli/src/flags.rs — add wait_until field + --wait-until parsing
• cli/src/commands.rs — pass waitUntil in navigate JSON command
• src/actions.ts — change default from load to domcontentloaded

Test plan

• Rust compiles without errors
• TypeScript compiles without errors
• open <url> completes faster on SPA sites
• open <url> --wait-until load preserves old behavior

Closes #479

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Additional Suggestion:

Native Rust daemon defaults to WaitUntil::Load for navigate and diff_url commands, while the Node.js daemon was changed to default to 'domcontentloaded', causing inconsistent behavior between the two daemon implementations.