Add sound effects, ambient music and volume mixing (0.5.0)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/audio/test_sound_catalog.gd

@@ -0,0 +1,44 @@
+extends GutTest
+## Chaque identifiant sonore pointe vers un fichier present ; un identifiant
+## inconnu ne produit jamais de chemin libre.
+
+
+func test_every_sfx_file_exists() -> void:
+    for sfx_id in SoundCatalog.SFX_IDS:
+        assert_true(ResourceLoader.exists(SoundCatalog.sfx_path(sfx_id)), sfx_id)
+
+
+func test_every_music_file_exists() -> void:
+    for music_id in SoundCatalog.MUSIC_IDS:
+        assert_true(ResourceLoader.exists(SoundCatalog.music_path(music_id)), music_id)
+
+
+func test_unknown_ids_give_no_path() -> void:
+    assert_eq(SoundCatalog.sfx_path("../../etc/passwd"), "")
+    assert_eq(SoundCatalog.music_path("inconnue"), "")
+
+
+func test_music_follows_the_level() -> void:
+    assert_eq(SoundCatalog.music_for_level("CE1"), "forest")
+    assert_eq(SoundCatalog.music_for_level("CE2"), "marsh")
+
+
+func test_audio_manager_plays_without_crashing_and_remembers_music() -> void:
+    AudioManager.play_sfx("success")
+    AudioManager.play_music("marsh")
+    assert_eq(AudioManager.current_music_id(), "marsh")
+    AudioManager.play_music("marsh")
+    AudioManager.stop_music()
+    assert_eq(AudioManager.current_music_id(), "")
+
+
+func test_buses_exist_and_are_idempotent() -> void:
+    AudioBuses.ensure()
+    AudioBuses.ensure()
+    assert_ne(AudioServer.get_bus_index(AudioBuses.MUSIC), -1)
+    assert_ne(AudioServer.get_bus_index(AudioBuses.EFFECTS), -1)
+    var count := 0
+    for i in AudioServer.bus_count:
+        if AudioServer.get_bus_name(i) == AudioBuses.MUSIC:
+            count += 1
+    assert_eq(count, 1)

tests/audio/test_sound_catalog.gd.uid

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+uid://c61j06k8itgcq