feat(editor): add WSTM JSON round-trip (--export/--import-wstm-json)

Closes the editing loop on the stat-modifier-curve catalog: dump
a .wstm to JSON, hand-edit baseValue / perLevelDelta /
multiplier / level range / curveKind (e.g. retune SpellCrit base
from 1%% to 1.5%% for a higher-magic server, halve the
ManaPerSpirit slope by setting multiplier=0.5, restrict an armor
curve to lvl 60+ only by raising minLevel), re-import to a
byte-identical binary.

curveKind dual-encoded: int 0..6 OR human-readable name ("crit"
/ "hit" / "power" / "regen" / "resist" / "mitigation" / "misc").
Float fields (baseValue, perLevelDelta, multiplier) round-trip
through JSON's native number type — IEEE 754 single precision
preserves exactly.

Verified byte-identical round-trip on all three presets
(crit / regen / armor). CLI flag count 1081 -> 1083.

tools/editor/cli_arg_required.cpp

@@ -290,6 +290,7 @@ const char* const kArgRequired[] = {
     "--export-wstc-json", "--import-wstc-json",
     "--gen-stm", "--gen-stm-regen", "--gen-stm-armor",
     "--info-wstm", "--validate-wstm",
+    "--export-wstm-json", "--import-wstm-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",