* fix: support URL parameter in tab new command
The CLI was correctly sending the URL parameter when running
`agent-browser tab new <url>`, but the TypeScript daemon was
ignoring it because:
1. The schema didn't include the url field (stripped during validation)
2. The TabNewCommand type didn't have a url property
3. The handler didn't pass the URL to browser.newTab()
4. browser.newTab() didn't accept or use a URL parameter
This fix adds URL support throughout the chain so that
`agent-browser tab new https://example.com` now correctly
opens a new tab and navigates to the specified URL.
Fixes#62
* fix: omit url field when not provided in tab new command
Previously, the CLI always sent "url": null when no URL was provided,
which caused Zod validation to fail with "Expected string, received null".
Now the url field is only included when a URL is actually provided.
Fixes issue reported by @ctate in PR review.
* refactor: move navigation logic from BrowserManager to handleTabNew
Address review feedback:
- Add .min(1) to URL validation for consistency with navigateSchema
- Keep BrowserManager.newTab() simple (single responsibility)
- Handle navigation in handleTabNew following same pattern as handleNavigate
