Add industrial metal soundtrack with seamless loop

- assets/audio/music/zombie_industrial_loop.ogg: 57.60 s Ogg Vorbis loop
  generated locally with YuE2-3B on the Tesla V100 (score written for this
  track; vocals removed with HTDemucs). The loop is spliced at the track's
  structural repeat with a 0.6 s crossfade: measured seam dip <= 1.6 dB.
- scripts/main.gd: "Music" AudioStreamPlayer at -11 dB, started at boot on
  desktop and on the start click on Web (browser autoplay policy). It forces
  stream.loop at runtime because the Web staging step re-imports the OGG with
  loop=false.
- tools/test_music.gd: soundtrack test (loop, length, volume, playback,
  still playing after player death).
- docs/MUSIC.md: source, loop construction, verification, licence.
- docs/WEB-DEPLOY.md: release ab6054111f5919a8 notes.

Initial commit of the project.

tools/nginx-zombie-fps.conf

@@ -0,0 +1,39 @@
+# Scope is limited to this game. Versioned resources are never overwritten.
+location ^~ /pub/zombie-fps/releases/ {
+    alias /home/debian/public_html/zombie-fps/releases/;
+    index index.html;
+    autoindex off;
+    types {
+        text/html html;
+        application/javascript js;
+        application/wasm wasm;
+        application/octet-stream pck;
+        image/png png;
+    }
+    default_type application/octet-stream;
+    gzip_static on;
+    gzip_vary on;
+    gzip_proxied any;
+    add_header Cache-Control "public, max-age=31536000, immutable";
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+}
+location ^~ /pub/zombie-fps/ {
+    alias /home/debian/public_html/zombie-fps/;
+    index index.html;
+    autoindex off;
+    types {
+        text/html html;
+        application/javascript js;
+        application/wasm wasm;
+        application/octet-stream pck;
+        image/png png;
+    }
+    default_type application/octet-stream;
+    gzip_static on;
+    gzip_vary on;
+    gzip_proxied any;
+    add_header Cache-Control "no-cache" always;
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+}