fix: harden worklet caching and build guard

Un-hashed libopenmpt.worklet.js was inheriting the immutable
1-year cache from /assets/, risking stale audio on chiptune3
bumps. Add a dedicated short-cache location for it.

Also fail closeBundle loudly if the worklet source vanishes,
instead of silently shipping a build with hanging audio.

nginx.conf

@@ -10,6 +10,13 @@ server {
     add_header X-Content-Type-Options nosniff;
     add_header Referrer-Policy no-referrer-when-downgrade;
 
+    # un-hashed file copied by chiptuneWorkletFix -- must not be immutable
+    location = /assets/libopenmpt.worklet.js {
+        add_header Cache-Control "public, max-age=86400";
+        add_header X-Content-Type-Options nosniff;
+        add_header Referrer-Policy no-referrer-when-downgrade;
+    }
+
     location /assets/ {
         # add_header is not inherited once a location declares its own
         add_header X-Content-Type-Options nosniff;

vite.config.ts

@@ -30,7 +30,11 @@ function chiptuneWorkletFix(): Plugin {
     },
     closeBundle() {
       const src = resolve('node_modules/chiptune3/libopenmpt.worklet.js')
-      if (!existsSync(src)) return
+      if (!existsSync(src)) {
+        throw new Error(
+          'chiptuneWorkletFix: libopenmpt.worklet.js not found — chiptune3 layout changed?',
+        )
+      }
       const dest = resolve(outDir, assetsDir, 'libopenmpt.worklet.js')
       copyFileSync(src, dest)
     },