fix: remove injected js-dos CSS/script on Play unmount to prevent style leaking into other pages

frontend/src/pages/Play.svelte

@@ -17,6 +17,8 @@
 
   let dosContainer;
   let dosCI = null;
+  let injectedLink = null;
+  let injectedScript = null;
 
   async function load() {
     loading = true;
@@ -44,6 +46,7 @@
     link.rel = "stylesheet";
     link.href = "https://v8.js-dos.com/latest/js-dos.css";
     document.head.appendChild(link);
+    injectedLink = link;
 
     // Load js-dos script from CDN
     if (!window.Dos) {
@@ -54,6 +57,7 @@
           s.onload = resolve;
           s.onerror = reject;
           document.head.appendChild(s);
+          injectedScript = s;
         });
       } catch {
         error = "Failed to load emulator. Check your internet connection.";
@@ -109,6 +113,15 @@
       if (dosContainer) {
         dosContainer.innerHTML = "";
       }
+      // Remove injected js-dos CSS so it doesn't corrupt other pages
+      if (injectedLink && injectedLink.parentNode) {
+        injectedLink.parentNode.removeChild(injectedLink);
+        injectedLink = null;
+      }
+      if (injectedScript && injectedScript.parentNode) {
+        injectedScript.parentNode.removeChild(injectedScript);
+        injectedScript = null;
+      }
     };
   });
 </script>