feat(browser): add extraArgs config for custom Chrome launch arguments

Adds a `browser.extraArgs` config option (string array) that is appended
to Chrome's launch arguments. This enables users to add stealth flags,
window size overrides, custom user-agent strings, or other Chrome flags
without patching the source code.

Example config:
  browser.extraArgs: ["--window-size=1920,1080", "--disable-infobars"]

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/browser/chrome.ts

@@ -217,6 +217,11 @@ export async function launchOpenClawChrome(
     // Stealth: hide navigator.webdriver from automation detection (#80)
     args.push("--disable-blink-features=AutomationControlled");
 
+    // Append user-configured extra arguments (e.g., stealth flags, window size)
+    if (resolved.extraArgs.length > 0) {
+      args.push(...resolved.extraArgs);
+    }
+
     // Always open a blank tab to ensure a target exists.
     args.push("about:blank");