feat(editor): add --gen-texture-caustics water-shimmer pattern

52nd procedural texture: water-surface caustics via four
superimposed sine waves running along x, y, x+y, and x-y.
Each wave is taken in absolute value before multiplication
so peaks shine on either side of the wave centerline,
giving the bright-line interference network you see on a
pool floor or sunlit shallow streambed.

Two-color lerp from bgHex (depth) to hiHex (highlight).
Default 24-pixel period reads at the right scale for water-
plane underlay; pass a smaller period for tighter ripple.

Useful as the floor texture under transparent water
volumes, magic-fountain pools, fish-tank ground plates,
ritual scrying basins, and any "submerged surface seen
through clear water" effect.

tools/editor/cli_help.cpp

@@ -137,6 +137,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Corrugated: smooth cosine ridges between bg and hi (sheet-metal roofing / siding)\n");
     std::printf("  --gen-texture-rope <out.png> <bgHex> <ropeHex> [period] [strandW] [W H]\n");
     std::printf("                         Rope: two interleaved sinusoidal strands with cylindrical highlight (twisted cordage)\n");
+    std::printf("  --gen-texture-caustics <out.png> <bgHex> <hiHex> [period] [W H]\n");
+    std::printf("                         Caustics: 4 superimposed sine waves (x/y/x+y/x-y) producing diamond-mesh water shimmer\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");