feat(audio): Audio.* standard library over a native AVAudioPlayer backend (#22)

Adds the Audio.* namespace and its platform backend, the audio subsystem #22 was
blocked on.

- runtime/native/audio.ll: the macOS backend, AVAudioPlayer driven through the
  objc runtime C ABI (no ObjC/C source), same style as cocoa.ll — snd_load /
  play / stop / playing / set_volume / set_rate. Spliced and linked with
  AVFoundation only when a windowed build actually uses Audio.* (needed_framework,
  since AVAudioPlayer is reached by name).
- runtime/native/audio.ludic: the Audio.* runtime — a handle table, master
  volume/pitch, a single music channel. load/play/play_sound/play_music/stop/
  stop_music/stop_all/volume/pitch/is_playing. Every native call is
  is_windowed()-guarded, so a headless build carries the API as no-ops (load
  returns 0, is_playing false) and needs no audio device.
- compiler: Audio.* namespace dispatch, g_uses_audio splice, snd_* intrinsics +
  declarations, and the conditional AVFoundation link in both the canonical
  (main.ludic) and dev-runner (x app) paths.
- docs: a full docs/language/audio section (10 method pages); check-impl green.
- test: examples/library/audio.ludic self-asserts the headless no-op path.

Playback is out-of-band and never feeds the deterministic sim, but triggers are
frame-driven so replays fire the same sounds. Reseeded; suites green (80 + 29).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/backend/emit_call.ludic

@@ -216,6 +216,21 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
     if (meth == "touch_y")      { bare = "input_touch_y";      push(labels, "index") }
     if (meth == "set_touch")    { bare = "input_set_touch";    push(labels, "index"); push(labels, "x"); push(labels, "y"); push(labels, "active") }
   }
+  # Audio.* (#22) — sfx/music playback over the platform audio backend
+  # (runtime/native/audio.ludic + audio.ll). Playback is out-of-band; the
+  # triggers are ordinary frame-driven calls, so a replay fires the same sounds.
+  if (ns == "Audio") {
+    if (meth == "load")       { bare = "audio_load";       push(labels, "path") }
+    if (meth == "play")       { bare = "audio_play";       push(labels, "id") }
+    if (meth == "play_sound") { bare = "audio_play";       push(labels, "id") }
+    if (meth == "play_music") { bare = "audio_play_music"; push(labels, "id") }
+    if (meth == "stop")       { bare = "audio_stop";       push(labels, "id") }
+    if (meth == "stop_music") { bare = "audio_stop_music" }
+    if (meth == "stop_all")   { bare = "audio_stop_all" }
+    if (meth == "volume")     { bare = "audio_volume";     push(labels, "v") }
+    if (meth == "pitch")      { bare = "audio_pitch";      push(labels, "v") }
+    if (meth == "is_playing") { bare = "audio_is_playing"; push(labels, "id") }
+  }
   # Phase 3: the bare reflection / networking / process builtins, namespaced.
   # Each is a pure alias — the callee is rewritten to the bare name below.
   if (ns == "World") {

selfhost/backend/emit_head.ludic

@@ -67,6 +67,12 @@ function emit_header() -> void {
   emith("declare void @win_mouse(ptr)\n")
   emith("declare void @win_pad(ptr)\n")
   emith("declare void @win_touch(ptr)\n")
+  emith("declare ptr @snd_load(ptr)\n")               # #22 audio backend (audio.ll)
+  emith("declare void @snd_play(ptr, i32, i32, i32)\n")
+  emith("declare void @snd_stop(ptr)\n")
+  emith("declare i32 @snd_playing(ptr)\n")
+  emith("declare void @snd_set_volume(ptr, i32)\n")
+  emith("declare void @snd_set_rate(ptr, i32)\n")
   emith("@__stderrp = external global ptr\n")
   emith("@__stdoutp = external global ptr\n")
   emith("@.fmt_int = private unnamed_addr constant [4 x i8] c\"%d\\0A\\00\"\n")

selfhost/backend/emit_intrin2.ludic

@@ -13,6 +13,8 @@ function is_intrinsic2(name: pointer) -> bool {
   if (name == "win_running") or (name == "win_close") { return true }
   if (name == "win_held") or (name == "win_mouse") { return true }   # #50 device layer
   if (name == "win_pad") or (name == "win_touch") { return true }    # #51 gamepad / touch
+  if (name == "snd_load") or (name == "snd_play") or (name == "snd_stop") { return true }   # #22 audio
+  if (name == "snd_playing") or (name == "snd_set_volume") or (name == "snd_set_rate") { return true }
   return false
 }
 
@@ -60,5 +62,15 @@ function emit_intrinsic2(name: pointer, e: Node) -> Val {
   # words/point [active, x, y]. Both windowed-only, DCE'd headless.
   if (name == "win_pad")   { let a = arg_code(e, 0);  emit("  call void @win_pad(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
   if (name == "win_touch") { let a = arg_code(e, 0);  emit("  call void @win_touch(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
+  # #22 audio backend — AVAudioPlayer via audio.ll; windowed-only, DCE'd headless.
+  if (name == "snd_load") { let a = arg_code(e, 0);  return val(emit_bind(`call ptr @snd_load(ptr {a})`), "pointer") }
+  if (name == "snd_play") {
+    let a = arg_code(e, 0);  let b = arg_code(e, 1);  let c = arg_code(e, 2);  let d = arg_code(e, 3)
+    emit("  call void @snd_play(ptr ");  emit(a);  emit(", i32 ");  emit(b);  emit(", i32 ");  emit(c);  emit(", i32 ");  emit(d);  emit(")\n");  return val("0", "void")
+  }
+  if (name == "snd_stop") { let a = arg_code(e, 0);  emit("  call void @snd_stop(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
+  if (name == "snd_playing") { let a = arg_code(e, 0);  return val(emit_bind(`call i32 @snd_playing(ptr {a})`), "int") }
+  if (name == "snd_set_volume") { let a = arg_code(e, 0);  let b = arg_code(e, 1);  emit("  call void @snd_set_volume(ptr ");  emit(a);  emit(", i32 ");  emit(b);  emit(")\n");  return val("0", "void") }
+  if (name == "snd_set_rate") { let a = arg_code(e, 0);  let b = arg_code(e, 1);  emit("  call void @snd_set_rate(ptr ");  emit(a);  emit(", i32 ");  emit(b);  emit(")\n");  return val("0", "void") }
   return val("0", "void")
 }