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.

export_presets.cfg

@@ -0,0 +1,29 @@
+[preset.0]
+name="Web"
+platform="Web"
+runnable=true
+advanced_options=false
+dedicated_server=false
+custom_features=""
+export_filter="all_resources"
+include_filter=""
+exclude_filter="addons/*,tools/*,docs/*,build/*,assets/**/*.mdl,assets/half_life_manifest.json"
+export_path="build/web/index.html"
+patches=PackedStringArray()
+encrypt_pck=false
+encrypt_directory=false
+script_export_mode=2
+
+[preset.0.options]
+custom_template/debug=""
+custom_template/release=""
+variant/extensions_support=false
+variant/thread_support=false
+vram_texture_compression/for_desktop=true
+vram_texture_compression/for_mobile=true
+html/export_icon=false
+html/custom_html_shell=""
+html/head_include="<meta name=\"description\" content=\"Zombie Room FPS — prototipo Godot. WASD, mouse, R ricarica.\">"
+html/canvas_resize_policy=2
+html/focus_canvas_on_start=true
+progressive_web_app/enabled=false