feat(ugc): draw player models' icons from their generated NIF

The icon was rendered from a second mesh built only for it (the icon
renderer's color corrections, no variation, occlusion worked out again). It
is now drawn from the .nif just made, read back with NifFile at LOD 0, so it
shows exactly what the game shows: the color variation, the removed faces and
the lighting baked into the vertex colors (so it adds no occlusion of its
own). icon_correct_colors and icon_color_variation are gone; the camera and
light settings stay. Cars and rockets are drawn as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/UgcServer.md

@@ -73,12 +73,13 @@ defaults. The table below goes through it step by step.
    blending. Opaque shapes are divided at 65535 vertices along their longest side (LU Toolbox's divide_mesh);
    transparent bricks are one shape each unless `combine_transparent=1`. Vertices are in LDD's Y-up space with
    identity transforms, like the game's own brick models.
-7. The icon is rendered like LU Toolbox's icon renderer (its UGC render add-on's BrickBuild scene) by a software
-   rasterizer (no GPU, no display), 4x4 supersampled: LOD 0 with the icon's color corrections (white and black toned
-   down) and no color variation, a 50 mm lens (39.6 degrees) from 53.4 degrees around and 19.5 above, framed at 1.03,
-   a sun of strength 2.5 from 21 degrees around and 50.3 above with soft shadows, and a grey (0.192) world light
-   darkened by the ambient occlusion, on a transparent background: `icon.png` for the dashboard and a 32-bit
-   `icon.dds` for the client.
+7. The icon is drawn from the finished `.nif`: it is read back with the same reader as the client's files (NifFile,
+   LOD 0) and rasterized, so it shows exactly what the game shows, with the color variation, the faces that were
+   removed and the lighting baked into the vertex colors (so the icon adds no occlusion of its own). The camera and
+   lights are LU Toolbox's icon renderer's (its UGC render add-on's BrickBuild scene), drawn by a software rasterizer
+   (no GPU, no display), 4x4 supersampled: a 50 mm lens (39.6 degrees) from 53.4 degrees around and 19.5 above,
+   framed at 1.03, a sun of strength 2.5 from 21 degrees around and 50.3 above with soft shadows, and a grey (0.192)
+   world light, on a transparent background: `icon.png` for the dashboard and a 32-bit `icon.dds` for the client.
 8. `stats.json` records the bricks, each LOD's triangles before and after hidden faces were removed, vertices,
    shapes, how long each step took and the settings used; `model.noao.nif` is LOD 0 before the lighting bake. Both,
    and the icon and mesh of the version before (`previous.*`), are for the dashboard's viewer.
@@ -108,9 +109,9 @@ defaults. The table below goes through it step by step.
 | Bake Lighting, AO Only: 64 AO samples, distance 5, transparent skipped, glow strength 3 x 2, smooth vertex colors | Same (`ao_samples`, `ao_distance`, `glow_strength`); smoothing averages a vertex's corners, and the occlusion is per vertex already |
 | NifTools export for LU: 20.3.0.9, user version 0 | Same |
 | Physics (`.hkx`) | Intentionally not done: `.hkx` requests answer 404, so the client makes its own |
-| Icon: LOD 0, no hidden face removal, its own color corrections, no color variation | Same (`icon_correct_colors`, `icon_color_variation=0`); LOD 0's hidden face removal is reused (it doesn't change what the camera sees) |
+| Icon: LOD 0 imported again with its own color corrections (white and black toned down) and no color variation | Different on purpose: the icon is drawn from the generated `.nif` (LOD 0), so it matches the game, variation and baked lighting included; no icon-only color corrections |
 | Icon: Bevel Edges and Subdivide | Not done (the rasterizer draws the bricks as they are) |
-| Icon: principled materials (roughness 0.16), hashed transparency, Cycles | Approximated: diffuse sun with soft shadow-mapped shadows plus world light with ambient occlusion; no highlights or bounced light; transparent bricks sorted and blended |
+| Icon: principled materials (roughness 0.16), hashed transparency, Cycles | Approximated: diffuse sun with soft shadow-mapped shadows plus world light (player models: their baked lighting; cars and rockets: ambient occlusion, `icon_ao`); no highlights or bounced light; transparent bricks sorted and blended |
 | Icon scene BrickBuild / Car: 50 mm lens, camera 53.4 / 19.5 degrees, sun 2.5 at 21 / 50.3, world 0.192, 128 px, framing 1.03, transparent film | Same (`icon_*`, `modular_icon_*`) |
 | Icon scene Rocket: 35 mm lens, other angles, two suns | Not done: rockets use the car camera |