feat(editor): add --gen-texture-stars night-sky pattern

Solid background fill plus randomly placed stars at varied
brightness — most stars dim (30-65% blend toward star color),
occasional bright stars (85-100% blend) — so the sky reads
with depth rather than as uniform noise. Exit log breaks down
how many bright vs faint stars actually landed.

Defaults: density=0.005 (~0.5% of pixels become stars), seed=1.
Useful for skybox top-faces, distant night sky planes, magical
constellation set dressing. Brings the procedural texture
pattern set to 26.

tools/editor/cli_help.cpp

@@ -79,6 +79,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Tree bark: vertical wavy streaks + dark vertical cracks (default density=0.04)\n");
     std::printf("  --gen-texture-clouds <out.png> <skyHex> <cloudHex> [seed] [coverage] [W H]\n");
     std::printf("                         Sky with puffy clouds: multi-octave noise thresholded by coverage (default 0.5)\n");
+    std::printf("  --gen-texture-stars <out.png> <bgHex> <starHex> [seed] [density] [W H]\n");
+    std::printf("                         Night sky with scattered stars (varied brightness, density 0..1, default 0.005)\n");
     std::printf("  --add-texture-to-zone <zoneDir> <png-path> [renameTo]\n");
     std::printf("                         Copy an existing PNG into <zoneDir> (optionally renaming it on the way in)\n");
     std::printf("  --gen-mesh <wom-base> <cube|plane|sphere|cylinder|torus|cone|ramp> [size]\n");