feat(audio): suport d'efectes (eco i reverb) per a sons puntuals

Afig una capa d'efectes oberta a la unitat d'àudio. Els sons puntuals
es poden reproduir processats per un eco o un reverb (Freeverb 8C/4AP)
sense afectar la música ni canviar el camí ràpid existent (playSound
sense efecte segueix sent una sola crida sense cost extra).

  - data/sounds.yaml: catàleg de presets nominats (echo: cave/short,
    reverb: stone_hall/small_room).
  - core/audio/audio_effects: processadors purs que prenen un Ja::Sound
    (U8/S16, mono o estèreo) i tornen PCM S16 amb la cua de l'efecte
    (cap a 800 ms eco, 1500 ms reverb).
  - core/audio/sound_effects_config: Meyers singleton que parseja
    sounds.yaml a EchoParams/ReverbParams indexats per nom; l'API
    pública d'Audio fa el lookup per nom.
  - jail_audio::Engine: nou camí playSoundWith{Echo,Reverb} que empenta
    el buffer ja processat a un canal lliure marcat com a has_effect.
    El cap MAX_EFFECT_CHANNELS limita a 4 sons amb efecte simultanis;
    si està al límit, l'engine retorna -1 i Audio cau a la versió seca.
  - Audio::playSoundWith{Echo,Reverb}(name, preset, group) com a única
    via pública. Si el preset no existeix, fallback dry amb avís.
  - director: load("data/sounds.yaml") abans d'Audio::init.

source/core/audio/jail_audio.cpp

@@ -4,6 +4,10 @@
 #include <cassert>
 #include <cstdio>
 #include <memory>
+#include <optional>
+#include <vector>
+
+#include "core/audio/audio_effects.hpp"
 
 // Només declaracions de stb_vorbis: STB_VORBIS_HEADER_ONLY omet el bloc
 // d'implementació. Les definicions les aporta source/external/stb_vorbis_impl.cpp
@@ -397,13 +401,17 @@ namespace Ja {
     }
 
     void Engine::stopChannel(const int channel) {
-        forEachTargetChannel(channel, [](Channel& ch) {
+        forEachTargetChannel(channel, [this](Channel& ch) {
             if (ch.state != ChannelState::FREE) {
                 if (ch.stream != nullptr) { SDL_DestroyAudioStream(ch.stream); }
                 ch.stream = nullptr;
                 ch.state = ChannelState::FREE;
                 ch.pos = 0;
                 ch.sound = nullptr;
+                if (ch.has_effect) {
+                    ch.has_effect = false;
+                    if (effect_channels_active_ > 0) { --effect_channels_active_; }
+                }
             }
         });
     }
@@ -438,6 +446,55 @@ namespace Ja {
         }
     }
 
+    auto Engine::playProcessedOnFreeChannel(const std::vector<std::uint8_t>& bytes, const SDL_AudioSpec& spec, const int group) -> int {
+        // El cap de canals amb efecte es valida abans de reservar slot —
+        // així evitem crear i destruir un stream només per descartar el play.
+        if (effect_channels_active_ >= MAX_EFFECT_CHANNELS) { return -1; }
+
+        int channel = 0;
+        while (channel < MAX_SIMULTANEOUS_CHANNELS && channels_[channel].state != ChannelState::FREE) { ++channel; }
+        if (channel == MAX_SIMULTANEOUS_CHANNELS) { channel = 0; }
+
+        stopChannel(channel);
+
+        // El stream es crea contra l'spec del buffer processat (S16, ...)
+        // perquè SDL faci el resampling cap a audio_spec_ del device.
+        channels_[channel].stream = SDL_CreateAudioStream(&spec, &audio_spec_);
+        if (channels_[channel].stream == nullptr) {
+            std::fprintf(stderr, "Ja::Engine::playProcessedOnFreeChannel: Failed to create audio stream!\n");
+            return -1;
+        }
+
+        channels_[channel].sound = nullptr;  // El buffer no és propietat de cap Ja::Sound.
+        channels_[channel].times = 0;
+        channels_[channel].pos = 0;
+        const int CLAMPED_GROUP = (group >= 0 && group < MAX_GROUPS) ? group : 0;
+        channels_[channel].group = CLAMPED_GROUP;
+        channels_[channel].state = ChannelState::PLAYING;
+        channels_[channel].has_effect = true;
+        ++effect_channels_active_;
+
+        SDL_PutAudioStreamData(channels_[channel].stream, bytes.data(), static_cast<int>(bytes.size()));
+        SDL_SetAudioStreamGain(channels_[channel].stream, sound_volume_[CLAMPED_GROUP]);
+        SDL_BindAudioStream(sdl_audio_device_, channels_[channel].stream);
+
+        return channel;
+    }
+
+    auto Engine::playSoundWithEcho(const Sound* sound, const EchoParams& params, const int group) -> int {
+        if (sound == nullptr) { return -1; }
+        auto processed = AudioEffects::applyEcho(*sound, params);
+        if (!processed) { return -1; }
+        return playProcessedOnFreeChannel(processed->bytes, processed->spec, group);
+    }
+
+    auto Engine::playSoundWithReverb(const Sound* sound, const ReverbParams& params, const int group) -> int {
+        if (sound == nullptr) { return -1; }
+        auto processed = AudioEffects::applyReverb(*sound, params);
+        if (!processed) { return -1; }
+        return playProcessedOnFreeChannel(processed->bytes, processed->spec, group);
+    }
+
     // --- Factories i destructors (permanents) ---
 
     auto loadMusic(const Uint8* buffer, Uint32 length) -> Music* {