Skip creating .setup.jsdos bundles for Windows games

- Move platform detection before setup bundle creation
- Only create setup bundle when platform != 'windows'
- Also hide the Setup button in GameDetail for Windows games
- Windows setup executables (INSTALL.EXE) can't run in DOSBox anyway

frontend/src/pages/GameDetail.svelte

@@ -232,7 +232,7 @@
                 ▶ Unplayable
               </button>
             {/if}
-            {#if game.has_setup}
+            {#if game.has_setup && game.platform !== 'windows'}
               <button class="btn btn-setup" onclick={handleSetup}>🛠 Setup</button>
             {/if}
             <button class="btn" onclick={startEdit}>✏ Edit</button>