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>

dDashboardServer/routes/SettingsCatalog.cpp

@@ -480,6 +480,7 @@ namespace {
 		c.Add(Float(UGC, "glitter_size", "Glitter tile size", "The fleck texture's tile in model units (a stud is 0.8): how far apart the flecks are, the same on every brick.", "1.6", 0.1f, 100));
 		c.Add(Int(UGC, "glitter_density", "Glitter flecks", "Flecks in one tile of the glitter texture.", "50", 0, 2000));
 		c.Add(Float(UGC, "glitter_speed", "Glitter speed", "How fast the flecks drift: 1 moves them a tile in 7 s one way and 11 s the other; 0 keeps them still.", "1", 0, 100));
+		c.Add(Bool(UGC, "glitter_random", "Glitter placed per brick", "Each glitter brick gets its own fleck pattern (turned and moved by a number of the brick's own, the same every time the model is made); off: the same pattern on every brick.", true));
 		c.Add(Text(UGC, "satin_colors", "Satin colors", "Satin (opal) color ids, comma separated: they stay transparent plastic (the client has no satin shader) but are made milky and less see-through. By default LEGO's satin colors 360,362,363,364,365,366,367,376 (none: off)." + notLive, "360,362,363,364,365,366,367,376"));
 		c.Add(Float(UGC, "satin_opacity", "Satin opacity", "Percent: the opacity of transparent satin bricks, instead of the transparent opacity.", "75", 0, 100));
 		c.Add(Float(UGC, "satin_whiten", "Satin whitening", "Percent: how far satin colors go towards white.", "20", 0, 100));