feat(editor): add WSPC JSON round-trip (--export/--import-wspc-json)

Closes the editing loop on the spell-power-cost bucket catalog:
dump a .wspc to JSON, hand-edit baseCost / perLevelCost /
percentOfBase / powerType / costFlags (e.g. retune LowMana from
5% to 4%, add ScalesWithMastery to a class bucket, switch a
Whirlwind cost from 25 rage to 20), re-import to a byte-identical
binary.

The exporter emits both powerType (int 0..11) and the human-
readable powerTypeName ("mana" / "rage" / "focus" / "energy" /
"happiness" / "runic-power" / "runes" / "soul-shards" /
"holy-power" / "eclipse" / "health" / "no-cost"). costFlags is
emitted as both int bitfield AND pipe-separated label string.
The importer prefers the int form for costFlags when both are
present so unknown flag bits round-trip losslessly.

Verified byte-identical round-trip on all three presets
(starter / rage / mixed). CLI flag count 927 -> 929.

tools/editor/cli_arg_required.cpp

@@ -224,6 +224,7 @@ const char* const kArgRequired[] = {
     "--export-wcef-json", "--import-wcef-json",
     "--gen-spc", "--gen-spc-rage", "--gen-spc-mixed",
     "--info-wspc", "--validate-wspc",
+    "--export-wspc-json", "--import-wspc-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",