fix: double return 0 in generated C output

- wcprogram.js.generateCode now checks if the body already contains
  a return or exit statement before appending the hardcoded return 0;
  This eliminates the duplicate return 0 from the END block.

wcprogram.js

@@ -237,6 +237,8 @@ class WCProgram extends HTMLElement {
           .filter(Boolean).map(s => s + "\n").join("")
       : "";
 
+    const hasReturnOrExit =
+      body.includes("\n  return ") || body.includes("\n  exit(");
     const raw =
       "// --- WiseCode\u00ae ---\n" +
       (includes ? includes + "\n\n" : "") +
@@ -244,7 +246,7 @@ class WCProgram extends HTMLElement {
       (typeDefs ? typeDefs + "\n\n" : "") +
       (unitDefs ? unitDefs + "\n\n" : "") +
       stringStruct + dataSection + body +
-      "return 0;\n" +
+      (hasReturnOrExit ? "" : "return 0;\n") +
       "}\n// --- END ---";
     outputEl.textContent = raw;
     if (typeof hljs !== "undefined") hljs.highlightElement(outputEl);