fix(ugc): each glitter brick gets its own fleck pattern

Every glitter brick had the same flecks in the same places: the UVs were
the vertex positions projected on an axis plane, so bricks a whole tile
apart (and every brick of the same shape at the same spot in its own
model) looked identical. Each brick now has a number of its own
(UgcGlitter::BrickSeed, from the model's id and the brick's index, kept
per vertex in Mesh::brickSeeds) that turns the projection by an angle
and moves it by an offset under a tile, differently for each axis
plane. A model made again gets the same patterns; every LOD of a brick
the same one. The icon now draws the flecks on the UVs the .nif has
(Mesh::uvs read back by FromNif). New setting glitter_random (1; 0 puts
the same pattern on every brick as before). Non-glitter models are
byte-identical (hash tests unchanged).

Check in game: reprocess a model with several glitter bricks of the
same shape; the fleck patterns differ from brick to brick.

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

dUgcServer/Model/UgcModel.h

@@ -50,6 +50,11 @@ namespace UgcModel {
 		std::vector<glm::vec4> colors; // sRGB, 0..1, alpha is opacity
 		std::vector<glm::vec3> glow;   // linear glow color per vertex (LU Toolbox's "Glow" layer); empty when nothing glows
 		std::vector<eLook> looks;      // per vertex; empty when everything is plastic (transparent meshes: plastic or glitter)
+		// Per vertex: its brick's UgcGlitter::BrickSeed, which places the brick's glitter; empty when not known (a
+		// mesh read from a .nif)
+		std::vector<uint32_t> brickSeeds;
+		// Per vertex: the UV set of a mesh read from a .nif (its glitter's, placed when it was made); empty otherwise
+		std::vector<glm::vec2> uvs;
 		std::vector<uint32_t> indices;
 
 		size_t TriangleCount() const { return indices.size() / 3; }