feat(editor): add --gen-texture-star solid polygon

79th procedural texture: solid N-pointed star polygon
centered on the texture. Each pixel computes its polar
(r, θ); the star boundary at any θ alternates between
outer and inner radii using a 2π/N triangular-wave pattern
(0 at sector edges = points, 1 at sector center = valley).
Pixels with r < boundary(θ) are filled with the star color.

Distinct from --gen-texture-starburst (thin rays with bg
between them) and --gen-texture-pinwheel (alternating
solid wedges) — star is a single solid polygon shape.

innerFrac controls the star's "sharpness": near 0 gives
spike-thin star arms; near 1 approximates a circle. Default
0.40 with 5 points gives the classic American-flag star.
The first point is rotated to the top (-Y screen direction)
for canonical orientation.

Useful for medallion centers, shield emblems, religious /
order symbols, magic-circle icons, banner emblems, sheriff-
badge inserts.

tools/editor/cli_arg_required.cpp

@@ -117,6 +117,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-embroidery", "--gen-texture-lightbeam",
     "--gen-texture-dewdrops", "--gen-texture-pinwheel",
     "--gen-texture-scratched-metal", "--gen-texture-crackle",
+    "--gen-texture-star",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",