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.

addons/goldsrc/importer/wad_importer.gd

@@ -0,0 +1,110 @@
+@tool
+extends EditorImportPlugin
+## Imports a GoldSrc WAD file.
+##
+## The WAD is saved as a minimal .tres marker so Godot tracks it as a known
+## asset. The BSP importer loads WAD files directly via the C++ GoldSrcWAD
+## class — it does not use extracted PNGs.
+##
+## PNG extraction is opt-in (extract_textures = false by default) for cases
+## where individual textures are needed outside of BSP rendering.
+
+
+func _get_importer_name() -> String:
+	return "goldsrc.wad"
+
+
+func _get_visible_name() -> String:
+	return "GoldSrc WAD"
+
+
+func _get_recognized_extensions() -> PackedStringArray:
+	return PackedStringArray(["wad"])
+
+
+func _get_save_extension() -> String:
+	return "tres"
+
+
+func _get_resource_type() -> String:
+	return "Resource"
+
+
+func _get_preset_count() -> int:
+	return 1
+
+
+func _get_preset_name(preset_index: int) -> String:
+	return "Default"
+
+
+func _get_priority() -> float:
+	return 1.0
+
+
+func _get_import_order() -> int:
+	return 0
+
+
+func _can_import_threaded() -> bool:
+	return false
+
+
+func _get_import_options(_path: String, _preset_index: int) -> Array[Dictionary]:
+	return [
+		{
+			"name": "extract_textures",
+			"default_value": false,
+		},
+		{
+			"name": "output_directory",
+			"default_value": "",
+			"property_hint": PROPERTY_HINT_DIR,
+			"hint_string": "Leave empty to extract next to the WAD file",
+		},
+	]
+
+
+func _get_option_visibility(_path: String, _option_name: StringName, _options: Dictionary) -> bool:
+	if _option_name == "output_directory":
+		return _options.get("extract_textures", true)
+	return true
+
+
+func _import(source_file: String, save_path: String, options: Dictionary,
+		_platform_variants: Array[String], _gen_files: Array[String]) -> Error:
+	var extract: bool = options.get("extract_textures", true)
+
+	var wad := GoldSrcWAD.new()
+	var err = wad.load_wad(source_file)
+	if err != OK:
+		push_error("WAD Importer: Failed to load '%s': %s" % [source_file, error_string(err)])
+		return err
+
+	if extract:
+		var output_dir: String = options.get("output_directory", "")
+		if output_dir.is_empty():
+			# Default: create a folder named after the WAD next to it
+			output_dir = source_file.get_base_dir().path_join(
+				source_file.get_file().get_basename())
+
+		DirAccess.make_dir_recursive_absolute(output_dir)
+
+		var names = wad.get_texture_names()
+		var count := 0
+		for tex_name in names:
+			var tex = wad.get_texture(tex_name)
+			if tex == null:
+				continue
+			var img = tex.get_image()
+			if img == null:
+				continue
+			var png_path := output_dir.path_join(tex_name.to_lower() + ".png")
+			img.save_png(png_path)
+			count += 1
+
+		print("WAD Importer: Extracted %d textures to %s" % [count, output_dir])
+
+	# Save a minimal marker resource so Godot considers the import complete
+	var res := Resource.new()
+	return ResourceSaver.save(res, save_path + "." + _get_save_extension())