feat: add browser configuration tool and fix STDIO mode

- Add browser_configure tool to change headless/headed mode, viewport, and user agent during session
- Fix STDIO entry point by preventing stdin close handlers in STDIO mode
- Fix headed mode default behavior when DISPLAY is available on Linux
- Add dynamic browser configuration update mechanism in Context class

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/config.ts

@@ -129,8 +129,10 @@ export function configFromCLIOptions(cliOptions: CLIOptions): Config {
   const launchOptions: LaunchOptions = {
     channel,
     executablePath: cliOptions.executablePath,
-    headless: cliOptions.headless,
   };
+  if (cliOptions.headless !== undefined) {
+    launchOptions.headless = cliOptions.headless;
+  }
 
   // --no-sandbox was passed, disable the sandbox
   if (cliOptions.sandbox === false)