feat(editor): add WSCD JSON round-trip (--export/--import-wscd-json)

Closes the editing loop on the spell-cooldown bucket catalog: dump
a .wscd to JSON, hand-edit cooldownMs / bucketKind / category
flags (e.g. retune the global cooldown from 1.5s to 1.0s, mark a
bucket as IgnoresCooldownReduction, add Polymorph variants to the
class family bucket), re-import to a byte-identical binary.

The exporter emits both bucketKind (int 0..4) and the human-
readable bucketKindName ("spell", "item", "class", "global",
"misc"); same dual form for categoryFlags (int bitfield AND
"AffectedByHaste|OnGCDStart" pipe-separated label string). The
importer prefers the int form for categoryFlags when both are
present so unknown flag bits round-trip losslessly, falling back
to the label form for hand-edited sidecars.

Verified byte-identical round-trip on all three presets
(starter / class / items). CLI flag count 912 -> 914.

tools/editor/cli_arg_required.cpp

@@ -217,6 +217,7 @@ const char* const kArgRequired[] = {
     "--export-wsdr-json", "--import-wsdr-json",
     "--gen-cdb", "--gen-cdb-class", "--gen-cdb-items",
     "--info-wscd", "--validate-wscd",
+    "--export-wscd-json", "--import-wscd-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",