fix(ugc): glitter flecks look like LEGO glitter

The fleck texture was 50 soft round blobs of one size, bright in the
middle and fading out, which read as a smudgy dot pattern. LEGO's glitter
bricks have many small flat flakes (about half a millimetre) of which
most look faint and a few catch the light. The flecks are now flat
flakes of glitter_fleck_size (0.05 model units, i.e. 0.5 mm; 0.7 to 1.3
of it) with a one-pixel edge, each as bright as its facet catches the
light (0.3 to 1 of glitter_fleck_opacity, 80%, weighted towards dim),
80 a tile by default. The texture grows (128 to 512) to keep a fleck 3
pixels wide. New settings glitter_fleck_size and glitter_fleck_opacity;
glitter_density defaults to 80. Only glitter output changes.

Check in game: reprocess a glitter model; close up, the flecks are small
crisp flakes of varied brightness, not blurry dots; from a few metres
the brick still reads as its color with a fine glitter.

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

resources/ugcconfig.ini

@@ -94,6 +94,8 @@ brushed_colors=298,300,1002,1004
 #   transparent ones, S<id>_GlitterAlpha_Model: 21 is LEGO-AnimUV, which lays a white fleck texture stored in the .nif
 #   over the color (still: the client never updates a placed model). 0: off, glitter stays plastic.
 # glitter_size: the fleck texture's tile in model units (a stud is 0.8); glitter_density: flecks in a tile;
+#   glitter_fleck_size: a fleck's diameter in model units (they are cm: 0.05 is half a millimetre, as LEGO's glitter);
+#   glitter_fleck_opacity: percent, the brightest flecks (each catches the light differently: most are dimmer).
 # shader_glitter_sparkle: the glitter bricks' sparkles, S<id>_GlitterSparkle_Model over both glitter groups (only with
 #   shader_glitter). 79 is Distortion Directional (Ocean), whose texture layers the client moves every frame on its
 #   own: a sparkle flashes where two layers' sparkles meet. (Nothing else can move on a placed model: the client never
@@ -109,7 +111,9 @@ shader_glitter=21
 glitter_material_types=glitter
 glitter_colors=114,117
 glitter_size=1.6
-glitter_density=50
+glitter_density=80
+glitter_fleck_size=0.05
+glitter_fleck_opacity=80
 shader_glitter_sparkle=79
 glitter_sparkle_size=0.1
 glitter_sparkle_amount=5