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/FEATURES.md

@@ -95,6 +95,8 @@ Characters and moving objects
 66. A PPM reader with box-filtered downscale (photo thumbnails) and word-wrapped overlay text — `texture.ludic` `tex_load_ppm`, `overlay.ludic` `ov_text_wrap`
 67. The overlay batches a whole frame into one upload and draws per texture range with optional scissor clips (per-change uploads stalled the driver: 40 ms -> 25 ms), plus nine-slice, rotated, line, disc and arc primitives — `overlay.ludic` `ov_flush`, `ov_clip`, `ov_nine`, `ov_sub_rot`, `ov_line`, `ov_disc`, `ov_arc`
 68. Weather on the daylight: an overcast factor greys and dims the sun and the sky's light, a fog multiplier thickens the air, a lightning flash — `daylight.ludic` `daylight_weather`
+69. An outline pass: an actor carries a rim width and colour, drawn as an inverted hull depth-tested against the scene, and anything that is not an actor can queue one at a transform (a scatter instance, a tile) — `actor.ludic` `actor_draw_outlines`, `outline_model`, `shaders/outline.frag`
+70. Two ways to make an island out of a survey: a radius from a centre, or the sea put around the survey's own edge with a noise-wobbled coast, both scaling the existing relief into the water and compressing the last few metres of height either side of the line into beach and shallows — `terrain.ludic` `terrain_island`, `terrain_coast`, `shaders/heightgen.frag`
 
 ## Against Unreal Engine 5 and RAGE (RDR2), honestly