feat: add page.stealth_evaluate() for undetectable JS execution (#108)

Extract CDP isolated world classes from humanize layer into standalone
stealth_eval module. Attach page.stealth_evaluate(expression) to every
page automatically — runs JS in a CDP isolated world with clean
Error.stack traces and full variable isolation from main world JS.

cloakbrowser/browser.py

@@ -138,6 +138,10 @@ def launch(
         cfg = resolve_config(human_preset, human_config)
         patch_browser(browser, cfg)
 
+    # Stealth evaluate — always attached
+    from .stealth_eval import patch_browser_stealth_eval
+    patch_browser_stealth_eval(browser, is_async=False)
+
     return browser
 
 
@@ -227,6 +231,10 @@ async def launch_async(  # noqa: C901
         cfg = resolve_config(human_preset, human_config)
         patch_browser_async(browser, cfg)
 
+    # Stealth evaluate — always attached
+    from .stealth_eval import patch_browser_stealth_eval
+    patch_browser_stealth_eval(browser, is_async=True)
+
     return browser
 
 
@@ -344,6 +352,10 @@ def launch_persistent_context(
         cfg = resolve_config(human_preset, human_config)
         patch_context(context, cfg)
 
+    # Stealth evaluate — always attached
+    from .stealth_eval import patch_context_stealth_eval
+    patch_context_stealth_eval(context, is_async=False)
+
     return context
 
 
@@ -463,6 +475,10 @@ async def launch_persistent_context_async(
         cfg = resolve_config(human_preset, human_config)
         patch_context_async(context, cfg)
 
+    # Stealth evaluate — always attached
+    from .stealth_eval import patch_context_stealth_eval
+    patch_context_stealth_eval(context, is_async=True)
+
     return context
 
 
@@ -556,6 +572,10 @@ def launch_context(
         cfg = resolve_config(human_preset, human_config)
         patch_context(context, cfg)
 
+    # Stealth evaluate — always attached
+    from .stealth_eval import patch_context_stealth_eval
+    patch_context_stealth_eval(context, is_async=False)
+
     return context