Add debug logging for Undefined symbol errors in sx.js

Logs env keys (non-function) when a symbol lookup fails, to help
diagnose which component/context is missing the expected binding.

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

shared/static/scripts/sx.js

@@ -418,6 +418,9 @@
       if (name === "true") return true;
       if (name === "false") return false;
       if (name === "nil") return NIL;
+      // Debug: log env keys to help diagnose
+      var envKeys = Object.keys(env).filter(function(k) { return typeof env[k] !== "function"; }).slice(0, 20);
+      console.error("Undefined symbol: " + name + " | env keys (non-fn): " + envKeys.join(", "));
       throw new Error("Undefined symbol: " + name);
     }