render3d: the reflection draws an actor when its mirror image is in view; reflection CPU in R3D_PROF

The water reflection keeps the main camera's frustum planes, and ac_visible tested the actor itself
against them: the town's people, far above the lake with their images far below the frame, all drew
again. The image (2L - y) is what is tested now - town, 69 skinned reflection draws -> 38, the frame
byte-identical; PC camp reflection scene CPU 793 -> about 760 us. R3D_PROF splits the reflection's
CPU into setup, terrain, scene and sky.

Tried and not kept, with the numbers (PC, camp, Vulkan GPU timestamps):
- the ground's cost is its scanned material taps: without them the terrain pass is 555 us of 1568,
  without the photograph 1029; the sun, the noise fields and the grain are 20-100 us each. Moving the
  cheap tier in from 200 m to 60 m changes nothing, so it is the far tier's single taps over the
  mountains. Skipping the normal-map taps past 900 m (where the detail normal is fully faded) saved
  22 us and moved a few pixels - reverted.
- grass: cutting its radius to 300 m barely moves it, so the cost is the near blades' pixels; moving
  their three noise fields to the vertices changed nothing (747 us) - reverted.

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

packages/ludic.render3d/water.ludic

@@ -78,9 +78,13 @@ function water_reflection_pass() -> void {
   let sb = sc_skip_blade
   sc_skip_blade = true                    # blades are invisible at this scale in a reflection
   ter_reflect = true
+  prof_cpu_mark("reflection setup")
   terrain_draw()
+  prof_cpu_mark("reflection terrain")
   scene_draw()
+  prof_cpu_mark("reflection scene")
   r3d_draw_sky()
+  prof_cpu_mark("reflection sky")
   ter_reflect = false
   sc_skip_blade = sb
   sc_freeze = false