fix: support URL parameter in tab new command (#64)

* 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

src/actions.ts

@@ -26,6 +26,7 @@ import type {
   SelectCommand,
   HoverCommand,
   ContentCommand,
+  TabNewCommand,
   TabSwitchCommand,
   TabCloseCommand,
   WindowNewCommand,
@@ -709,10 +710,17 @@ async function handleClose(
 }
 
 async function handleTabNew(
-  command: Command & { action: 'tab_new' },
+  command: TabNewCommand,
   browser: BrowserManager
 ): Promise<Response<TabNewData>> {
   const result = await browser.newTab();
+
+  // Navigate to URL if provided (same pattern as handleNavigate)
+  if (command.url) {
+    const page = browser.getPage();
+    await page.goto(command.url, { waitUntil: 'domcontentloaded' });
+  }
+
   return successResponse(command.id, result);
 }