feat(editor): WCST JSON round-trip closure

Adds --export-wcst-json / --import-wcst-json. Eight uint stat
fields per entry serialize as JSON ints; className field on
export is informational (classId is the authoritative key).
All 3 presets (warrior/mage/starting) byte-identical binary
roundtrip OK including the 9-entry starting-stats preset that
spans 9 different vanilla classes.

Live-tested monotonicity validator: hand-mutated Mage L20
baseStrength to 21 (below L10=22), validator correctly emitted:
"monotonicity: Mage baseStrength regresses from 22 (L10) to 21
(L20) — likely typo". The level-sorting + adjacent-pair walk
correctly identified the violation across the sparse 6-level
sample.

CLI flag count 1371 -> 1373.

tools/editor/cli_arg_required.cpp

@@ -400,6 +400,7 @@ const char* const kArgRequired[] = {
     "--export-wprt-json", "--import-wprt-json",
     "--gen-cst-warrior", "--gen-cst-mage", "--gen-cst-starting",
     "--info-wcst", "--validate-wcst",
+    "--export-wcst-json", "--import-wcst-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",