ix-mcp playwright instructions default to reusing a browser

The ix-mcp session instructions now tell the model to reuse a browser rather than launch a fresh Chromium every call. A new launch per turn wastes startup time and discards cookies and logins.

Within one session the persistent event loop keeps a launched browser and its state alive, so the recipe launches once and keeps the handle in a module global:

from playwright.async_api import async_playwright

if "browser" not in globals():
    p = await async_playwright().start()
    browser = await p.chromium.launch()
page = await browser.new_page()

To share one browser across separate sessions, the instructions connect over CDP (Chromium only). The connect-vs-launch decision rides on a recorded endpoint file, not a swallowed exception: the first session launches a persistent Chromium on a fixed --remote-debugging-port, records the endpoint, and later sessions read it and connect_over_cdp to the running browser via browser.contexts[0]. A stale endpoint raises on connect rather than silently relaunching, so the failure is visible.