refactor(core/audio): remove engine enable flags (INCONS-05)

Ja::Engine tenia music_enabled_ i sound_enabled_ com a membres amb el
seu propi enableMusic/enableSound setter, i disseminava checks
`if (!music_enabled_)` / `if (!sound_enabled_)` per gairebé totes les
operacions. Després del commit 3, ningú crida aquests setters: Audio
gestiona el gating per gain (effectiveVolume retorna 0 quan
music_enabled_/sound_enabled_ d'Audio són false). L'usuari ha confirmat
que vol mantenir aquesta semàntica (silenciar per gain, no parar).

Es retira tot el camí mort:

  - Membres music_enabled_ / sound_enabled_ eliminats.
  - Mètodes Engine::enableMusic(bool) / Engine::enableSound(bool)
    eliminats.
  - Checks `if (!music_enabled_)` / `if (!sound_enabled_)` eliminats de
    playMusic, pauseMusic, resumeMusic, fadeOutMusic, crossfadeMusic,
    updateCurrentMusic, playSound, playSoundOnChannel, pauseChannel,
    resumeChannel, updateSoundChannels.
  - Enum MusicState::DISABLED eliminat (inabastable sense el flag).
  - Enum ChannelState::INVALID i SOUND_DISABLED eliminats (no usats
    després de DEAD-04).
  - Audio::getMusicState treu el case DISABLED del switch.

Audio::enableMusic/enableSound i els seus flags music_enabled_/
sound_enabled_ d'Audio romanen — són ells els qui porten la decisió al
motor via setXxxVolume(config_.X_volume) → effectiveVolume → gain.
Tanca la meitat restant d'INCONS-05.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

source/core/audio/jail_audio.cpp

@@ -145,7 +145,7 @@ namespace Ja {
     }
 
     void Engine::updateCurrentMusic() {
-        if (!music_enabled_ || current_music_ == nullptr || current_music_->state != MusicState::PLAYING) { return; }
+        if (current_music_ == nullptr || current_music_->state != MusicState::PLAYING) { return; }
 
         updateIncomingFade();
 
@@ -156,8 +156,6 @@ namespace Ja {
     }
 
     void Engine::updateSoundChannels() {
-        if (!sound_enabled_) { return; }
-
         for (int i = 0; i < MAX_SIMULTANEOUS_CHANNELS; ++i) {
             if (channels_[i].state != ChannelState::PLAYING) { continue; }
 
@@ -214,7 +212,7 @@ namespace Ja {
     }
 
     void Engine::playMusic(Music* music, const int loop) {
-        if (!music_enabled_ || music == nullptr || music->vorbis == nullptr) { return; }
+        if (music == nullptr || music->vorbis == nullptr) { return; }
 
         stopMusic();
 
@@ -240,7 +238,6 @@ namespace Ja {
     }
 
     void Engine::pauseMusic() {
-        if (!music_enabled_) { return; }
         if (current_music_ == nullptr || current_music_->state != MusicState::PLAYING) { return; }
 
         current_music_->state = MusicState::PAUSED;
@@ -248,7 +245,6 @@ namespace Ja {
     }
 
     void Engine::resumeMusic() {
-        if (!music_enabled_) { return; }
         if (current_music_ == nullptr || current_music_->state != MusicState::PAUSED) { return; }
 
         current_music_->state = MusicState::PLAYING;
@@ -276,7 +272,6 @@ namespace Ja {
     }
 
     void Engine::fadeOutMusic(const int milliseconds) {
-        if (!music_enabled_) { return; }
         if (current_music_ == nullptr || current_music_->state != MusicState::PLAYING) { return; }
 
         stealCurrentIntoOutgoing(milliseconds);
@@ -284,7 +279,7 @@ namespace Ja {
     }
 
     void Engine::crossfadeMusic(Music* music, const int crossfade_ms, const int loop) {
-        if (!music_enabled_ || music == nullptr || music->vorbis == nullptr) { return; }
+        if (music == nullptr || music->vorbis == nullptr) { return; }
 
         stealCurrentIntoOutgoing(crossfade_ms);
 
@@ -312,7 +307,6 @@ namespace Ja {
     }
 
     auto Engine::getMusicState() const -> MusicState {
-        if (!music_enabled_) { return MusicState::DISABLED; }
         if (current_music_ == nullptr) { return MusicState::INVALID; }
         return current_music_->state;
     }
@@ -325,11 +319,6 @@ namespace Ja {
         return music_volume_;
     }
 
-    void Engine::enableMusic(const bool value) {
-        if (!value && current_music_ != nullptr && (current_music_->state == MusicState::PLAYING)) { stopMusic(); }
-        music_enabled_ = value;
-    }
-
     void Engine::onMusicDeleted(const Music* music) {
         if (music == nullptr) { return; }
         if (current_music_ == music) {
@@ -341,7 +330,7 @@ namespace Ja {
     // --- Sound ---
 
     auto Engine::playSound(Sound* sound, const int loop, const int group) -> int {
-        if (!sound_enabled_ || sound == nullptr) { return -1; }
+        if (sound == nullptr) { return -1; }
 
         int channel = 0;
         while (channel < MAX_SIMULTANEOUS_CHANNELS && channels_[channel].state != ChannelState::FREE) { channel++; }
@@ -354,7 +343,7 @@ namespace Ja {
     }
 
     auto Engine::playSoundOnChannel(Sound* sound, const int channel, const int loop, const int group) -> int {
-        if (!sound_enabled_ || sound == nullptr) { return -1; }
+        if (sound == nullptr) { return -1; }
         if (channel < 0 || channel >= MAX_SIMULTANEOUS_CHANNELS) { return -1; }
 
         stopChannel(channel);
@@ -380,7 +369,6 @@ namespace Ja {
     }
 
     void Engine::pauseChannel(const int channel) {
-        if (!sound_enabled_) { return; }
         forEachTargetChannel(channel, [](Channel& ch) {
             if (ch.state == ChannelState::PLAYING) {
                 ch.state = ChannelState::PAUSED;
@@ -390,7 +378,6 @@ namespace Ja {
     }
 
     void Engine::resumeChannel(const int channel) {
-        if (!sound_enabled_) { return; }
         const SDL_AudioDeviceID DEVICE = sdl_audio_device_;
         forEachTargetChannel(channel, [DEVICE](Channel& ch) {
             if (ch.state == ChannelState::PAUSED) {
@@ -435,13 +422,6 @@ namespace Ja {
         return V;
     }
 
-    void Engine::enableSound(const bool value) {
-        if (!value) {
-            stopChannel(-1);
-        }
-        sound_enabled_ = value;
-    }
-
     void Engine::onSoundDeleted(const Sound* sound) {
         if (sound == nullptr) { return; }
         for (int i = 0; i < MAX_SIMULTANEOUS_CHANNELS; ++i) {