feat(editor): add WSND JSON round-trip authoring workflow

Closes the WSND open-format loop with --export-wsnd-json /
--import-wsnd-json, mirroring the WOL/WOW/WOMX JSON pairs
from earlier batches.

Each entry round-trips all 9 fields:
  soundId, kind (int + kindName string), flags (int +
  flagsList string array), volume, minDistance, maxDistance,
  filePath, label.

Both kind and flags are emitted in dual form (int + named):
  • kind     : 2,
    kindName : "ambient",
  • flags    : 3,
    flagsList: ["loop", "3d"]

The importer accepts either form per field, so a hand-author
can write only the named string forms and skip the integer
boilerplate. Missing optional fields fall back to
WoweeSound::Entry defaults.

Verified byte-identical round-trip on the tavern preset
(5 entries with mixed flags and 3D distances).

Adds 2 flags (467 kArgRequired entries total). All 4 binary
formats added in recent batches now have full JSON round-trip:
WOL, WOW, WOMX, WSND.

tools/editor/cli_arg_required.cpp

@@ -28,6 +28,7 @@ const char* const kArgRequired[] = {
     "--gen-sound-catalog", "--gen-sound-catalog-ambient",
     "--gen-sound-catalog-tavern",
     "--info-wsnd", "--validate-wsnd",
+    "--export-wsnd-json", "--import-wsnd-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",