Blocking synchronous I/O (time.sleep, urllib) inside async event loop degrades performance

Description

In \local_browser.py, several synchronous I/O operations run inside async methods, blocking the asyncio event loop:

1. _is_local_cdp_available()\ (line 58) and _local_cdp_page_targets()\ (line 73) use \urllib.request\ synchronously
2. _ensure_local_cdp_browser()\ (line 262) uses \ ime.sleep(0.2)\ in a polling loop, blocking the loop for up to 10 seconds
3. _ensure_local_cdp_page_target()\ (line 93) uses synchronous urllib

\httpx\ is already listed as a dependency in \pyproject.toml\ (line 11) but isn't used anywhere.

Impact

• The event loop is blocked during CDP browser startup for up to 10 seconds
• \ ime.sleep()\ is not interruptible (unlike \syncio.sleep())
• Concurrent operations on the same event loop cannot make progress
• The polling loop cannot be cancelled mid-wait

Suggested Fix

Replace the synchronous helpers with async versions using \httpx.AsyncClient, convert _ensure_local_cdp_browser\ to async, and use \syncio.sleep()\ instead of \ ime.sleep().

The fix is straightforward since httpx is already a project dependency.

Start in local_browser.py at _is_local_cdp_available(), _local_cdp_page_targets(), _ensure_local_cdp_page_target(), and _ensure_local_cdp_browser(); inspect how these helpers are called and review the existing httpx dependency in pyproject.toml. Replace blocking HTTP and sleep operations with async equivalents, then verify CDP startup does not block or prevent cancellation of the polling loop.