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.

assets/zombies/zombie.mdl.import

@@ -0,0 +1,16 @@
+[remap]
+
+importer="goldsrc.mdl"
+importer_version=2
+type="PackedScene"
+uid="uid://1prmv1p8ow4f"
+path="res://.godot/imported/zombie.mdl-d906e37581a38c818d6d42ba6e40c16e.scn"
+
+[deps]
+
+source_file="res://assets/zombies/zombie.mdl"
+dest_files=["res://.godot/imported/zombie.mdl-d906e37581a38c818d6d42ba6e40c16e.scn"]
+
+[params]
+
+scale_factor=0.025

assets/zombies/zombie_textured.mdl.import

@@ -0,0 +1,16 @@
+[remap]
+
+importer="goldsrc.mdl"
+importer_version=2
+type="PackedScene"
+uid="uid://b7y3p1hlurwwt"
+path="res://.godot/imported/zombie_textured.mdl-e0bbc3f29995d7f67c65b7463a8e63be.scn"
+
+[deps]
+
+source_file="res://assets/zombies/zombie_textured.mdl"
+dest_files=["res://.godot/imported/zombie_textured.mdl-e0bbc3f29995d7f67c65b7463a8e63be.scn"]
+
+[params]
+
+scale_factor=0.025

assets/zombies/zombiet.mdl.import

@@ -0,0 +1,16 @@
+[remap]
+
+importer="goldsrc.mdl"
+importer_version=2
+type="PackedScene"
+uid="uid://ddvh548teagix"
+path="res://.godot/imported/zombiet.mdl-4a075fb2bbf6efbdad30d722ffef9e6b.scn"
+
+[deps]
+
+source_file="res://assets/zombies/zombiet.mdl"
+dest_files=["res://.godot/imported/zombiet.mdl-4a075fb2bbf6efbdad30d722ffef9e6b.scn"]
+
+[params]
+
+scale_factor=0.025