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>

packages/ludic.render3d/terrain.ludic

@@ -72,12 +72,36 @@ function terrain_lake(level: int, cx: int, cz: int, ex: int, ez: int) -> void {
 # over `fall` metres and on down to a shelf. Scaling rather than blending to a fixed bed is
 # what makes the coastline come out of the terrain that is already there — low ground turns
 # into beach and shallows, high ground into cliff. `r = 0` leaves the survey alone.
+const TER_ISLE_NONE: int = 0
+const TER_ISLE_RADIAL: int = 1
+const TER_ISLE_COAST: int = 2
 var ter_isle_cx: int = 0
 var ter_isle_cz: int = 0
 var ter_isle_r: int = 0
 var ter_isle_fall: int = 0
+var ter_isle_mode: int = 0
 function terrain_island(cx: int, cz: int, r: int, fall: int) -> void {
   ter_isle_cx = cx;  ter_isle_cz = cz;  ter_isle_r = r;  ter_isle_fall = fall
+  ter_isle_mode = TER_ISLE_RADIAL
+  if r == 0 { ter_isle_mode = TER_ISLE_NONE }
+}
+# The other way to make an island, and the one a real survey usually wants: put the sea
+# around the survey's OWN EDGE rather than cutting a circle out of the middle of it.
+# Everything the data covers stays land; the outer `margin` metres are under water and the
+# `fall` metres inside that are scaled down into it, exactly as terrain_island scales.
+#
+# The difference matters more than it sounds. Measuring a radius from a point in the middle
+# of an 8 km mountain survey drowns most of the survey to make an island of the rest —
+# you paid for the data and then threw two thirds of it away. Measuring inward from the
+# boundary keeps all of it and puts the coast where the data runs out, which is also where
+# a surveyor would tell you it runs out.
+#
+# The band is wobbled by low-frequency noise so the coastline is headlands and bays rather
+# than the square the data arrived in. `margin = 0` leaves the survey alone.
+function terrain_coast(cx: int, cz: int, margin: int, fall: int) -> void {
+  ter_isle_cx = cx;  ter_isle_cz = cz;  ter_isle_r = margin;  ter_isle_fall = fall
+  ter_isle_mode = TER_ISLE_COAST
+  if margin == 0 { ter_isle_mode = TER_ISLE_NONE }
 }
 
 # Use a real place: a 16-bit PNG height map plus its elevation range (metres). The
@@ -206,6 +230,7 @@ function terrain_generate() -> void {
     u_f4(gl_uniform(p, "u_lake"), ter_lake_cx, ter_lake_cz, ter_lake_ex, ter_lake_ez)
     u_f(gl_uniform(p, "u_lake_level"), ter_lake_level)
     u_f4(gl_uniform(p, "u_isle"), ter_isle_cx, ter_isle_cz, ter_isle_r, ter_isle_fall)
+    u_f(gl_uniform(p, "u_isle_mode"), fi(ter_isle_mode))
     u_f(gl_uniform(p, "u_dem_blur"), ter_dem_blur)
   }
   mesh_draw(sky_fullscreen)