feat(browser): use persistent Playwright connections for remote profile tab operations

For remote CDP profiles (e.g., Browserless), tab operations now use Playwright's
persistent connection instead of stateless HTTP requests. This ensures tabs
persist across operations rather than being terminated after each request.

Changes:
- pw-session.ts: Add listPagesViaPlaywright, createPageViaPlaywright, and
  closePageByTargetIdViaPlaywright functions using the cached Playwright connection
- pw-ai.ts: Export new functions for dynamic import
- server-context.ts: For remote profiles (!cdpIsLoopback), use Playwright-based
  tab operations; local profiles continue using HTTP endpoints
- server-context.ts: Fix ensureTabAvailable to not require wsUrl for remote
  profiles since Playwright accesses pages directly

This is a follow-up to #895 which added authentication support for remote CDP
profiles. The original PR description mentioned switching to persistent Playwright
connections for tab operations, but only the auth changes were merged.

src/browser/pw-ai.ts

@@ -1,8 +1,11 @@
 export {
   type BrowserConsoleMessage,
+  closePageByTargetIdViaPlaywright,
   closePlaywrightBrowserConnection,
+  createPageViaPlaywright,
   ensurePageState,
   getPageForTargetId,
+  listPagesViaPlaywright,
   refLocator,
   type WithSnapshotForAI,
 } from "./pw-session.js";