feat: SETUP.EXE detection + separate setup .jsdos bundle

When a game archive contains SETUP.EXE, INSTALL.EXE, CONFIG.EXE or
CUSTOM.EXE (or .com/.bat variants), the upload now:

- Detects and stores the path in game metadata (setup_exe / has_setup)
- Generates a second .jsdos bundle with SETUP.EXE as autoexec:
  - Standard mode: {gameId}.setup.jsdos (full game + setup autoexec)
  - Sockdrive mode: .jsdos-setup/ directory alongside .jsdos/
- Both bundles share the same game files; only the autoexec differs

Frontend changes:
- Router strips query params from hash so ?setup=1 doesn't leak into id
- GameDetail shows a "Setup" button between Play and Edit (only when
  game.has_setup is true), navigating to /play/{id}?setup=1
- Play.svelte detects ?setup=1, loads setupBundleUrl() instead, and
  shows setup-specific overlay text

Persistence is handled automatically by js-dos v8 via the built-in
auto-save mechanism (ci.persist() → browser OPFS), so any config
changes made via SETUP.EXE survive across sessions.

frontend/src/App.svelte

@@ -10,7 +10,8 @@
 
   function parseHash() {
     const hash = window.location.hash.slice(1) || "/";
-    const parts = hash.split("/").filter(Boolean);
+    const [pathPart] = hash.split("?"); // strip query params
+    const parts = pathPart.split("/").filter(Boolean);
     if (parts.length === 0 || (parts.length === 1 && parts[0] === "")) {
       route = "/";
       gameId = null;