fix(macOS): add JavaScript error capture (window.onerror + unhandledrejection)

CRITICAL DISCOVERY:
- index.html already has JSBI polyfills correctly applied (488 JSBI.BigInt calls) ✅
- JavaScript basic execution works (console.log confirmed in Player.log) ✅
- BUT game-bridge never initializes ('index.ts loaded' never appears) ❌

HYPOTHESIS:
game-bridge code fails silently during execution. No errors visible because:
1. Errors aren't being logged to Unity console
2. Promise rejections may be swallowed

FIX:
Add comprehensive error handlers in ImmutableWebView.mm:
1. window.onerror - catches synchronous JavaScript errors
2. unhandledrejection event - catches unhandled promise rejections
3. Both forward errors to Unity console via messageHandlers.logHandler

NEXT STEP:
With error capture, we'll see EXACTLY where game-bridge fails in next test run.

Author: rodrigo-fournier-immutable

Plugins/Mac/Sources/ImmutableWebView.mm

@@ -126,6 +126,18 @@ - (id)initWithUa:(const char *)ua
                 originalLog.apply(console, arguments); \
             }; \
         })(); \
+        window.onerror = function(msg, url, line, col, error) { \
+            var errorMsg = 'JS ERROR: ' + msg + ' at ' + url + ':' + line + ':' + col; \
+            if (error && error.stack) errorMsg += '\\nStack: ' + error.stack; \
+            try { window.webkit.messageHandlers.logHandler.postMessage(errorMsg); } catch(e) {} \
+            console.error(errorMsg); \
+            return false; \
+        }; \
+        window.addEventListener('unhandledrejection', function(e) { \
+            var errorMsg = 'UNHANDLED PROMISE REJECTION: ' + (e.reason ? e.reason.toString() : 'unknown'); \
+            try { window.webkit.messageHandlers.logHandler.postMessage(errorMsg); } catch(ex) {} \
+            console.error(errorMsg); \
+        }); \
         ";
 
     WKUserScript *script