feat: per-voice audio, outlines for what is not an actor, and a coast

Three things a game could not say, each of which had been worked around.

Audio.play_at(id, gain:, pitch:, pan:) fires a one-shot with its own gain,
pitch and stereo position. Audio.volume and Audio.pitch are global - they are
the options screen - so a game placing a sound in the world was fighting them,
and distance attenuation was simply not expressible. The backend already took
volume and rate per call; this adds setPan: alongside them and stops routing
through the master state.

ludic.render3d gains outline_model(model, mat, width, r, g, b): a rim around
something that is not an Actor. The outline pass walked the actor list and
stopped, so instanced scatter - a forest - could not be highlighted at all. It
is a queue flushed by the same pass, which is what gets the depth test right
when the caller does not control pass order.

And terrain_coast(cx, cz, margin, fall), the other way to make an island:
the sea around the survey's own edge rather than cut out of the middle of it.
terrain_island measures a radius from a centre, which drowns two thirds of a
real survey to make an island of the rest; this measures inward from the
boundary, so everything the data covers stays land and the coast is where the
data runs out. Both modes gained a strand - the last few metres of height
either side of the water line compressed, which stretches a cliff plunge out
into beach and shallows.

132 regression tests and the self-host fixpoints pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

selfhost/backend/emit_call.ludic

@@ -474,6 +474,10 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
     # Audio.play / play_music take a handle, or a name from the sound bank (Audio.define)
     if (meth == "play")       { if first_arg_is_text(e) { bare = "audio_play_named";  push(labels, "name") } else { bare = "audio_play";  push(labels, "id") } }
     if (meth == "play_sound") { bare = "audio_play";       push(labels, "id") }
+    # Audio.play_at(id, gain:, pitch:, pan:) — one shot with its own gain, pitch and
+    # stereo position. Audio.volume / Audio.pitch stay global (they are the options
+    # screen); this is the per-voice one, and it is what distance attenuation is built on.
+    if (meth == "play_at")    { bare = "audio_play_at";    push(labels, "id"); push(labels, "gain"); push(labels, "pitch"); push(labels, "pan") }
     if (meth == "play_music") { if first_arg_is_text(e) { bare = "audio_play_music_named";  push(labels, "name") } else { bare = "audio_play_music";  push(labels, "id") } }
     if (meth == "stop")       { bare = "audio_stop";       push(labels, "id") }
     if (meth == "stop_music") { bare = "audio_stop_music" }

selfhost/backend/emit_head.ludic

@@ -115,6 +115,7 @@ function emit_header() -> void {
   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("declare void @snd_set_pan(ptr, i32)\n")
   emith("declare ptr @hs_req_new(ptr, ptr)\n")          # #6 HTTP transport (http.ll)
   emith("declare void @hs_req_header(ptr, ptr, ptr)\n")
   emith("declare void @hs_req_body(ptr, ptr, i32)\n")

selfhost/backend/emit_intrin2.ludic

@@ -15,7 +15,7 @@ function is_intrinsic2(name: pointer) -> bool {
   if (name == "win_pad") or (name == "win_touch") { return true }    # #51 gamepad / touch
   if (name == "win_cursor_mode") { return true }                     # #89 cursor capture
   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 }
+  if (name == "snd_playing") or (name == "snd_set_volume") or (name == "snd_set_rate") or (name == "snd_set_pan") { return true }
   if (name == "hs_req_new") or (name == "hs_req_header") or (name == "hs_req_body") { return true }   # #6 HTTP
   if (name == "hs_send") or (name == "hs_done") or (name == "hs_status") or (name == "hs_body") { return true }
   if (name == "hs_blen") or (name == "hs_header") or (name == "hs_free") { return true }
@@ -78,6 +78,7 @@ function emit_intrinsic2(name: pointer, e: Node) -> Val {
   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") }
+  if (name == "snd_set_pan") { let a = arg_code(e, 0);  let b = arg_code(e, 1);  emit("  call void @snd_set_pan(ptr ");  emit(a);  emit(", i32 ");  emit(b);  emit(")\n");  return val("0", "void") }
   # #6 HTTP transport — NSURLConnection on a background thread (http.ll).
   if (name == "hs_req_new") { let a = arg_code(e, 0);  let b = arg_code(e, 1);  return val(emit_bind(`call ptr @hs_req_new(ptr {a}, ptr {b})`), "pointer") }
   if (name == "hs_req_header") { let a = arg_code(e, 0);  let b = arg_code(e, 1);  let c = arg_code(e, 2);  emit("  call void @hs_req_header(ptr ");  emit(a);  emit(", ptr ");  emit(b);  emit(", ptr ");  emit(c);  emit(")\n");  return val("0", "void") }