feat(editor): add WMAR JSON round-trip (--export/--import-wmar-json)

Dual encoding for markerKind (int 0..3 OR token
"raidtarget"/"worldmap"/"party"/"custom"). iconPath and
displayChar serialize as plain JSON strings for direct
authoring.

The displayChar field round-trip preserves exact byte
content — important since chat-overlay glyphs may
include short Unicode sequences (the Diamond marker
uses "<>" as a 2-char ASCII fallback for its glyph
rendering).

All 3 presets (raid/world/party) byte-identical
roundtrip OK. CLI flag count 1246 -> 1248.

tools/editor/cli_arg_required.cpp

@@ -361,6 +361,7 @@ const char* const kArgRequired[] = {
     "--export-wwfl-json", "--import-wwfl-json",
     "--gen-mar", "--gen-mar-world", "--gen-mar-party",
     "--info-wmar", "--validate-wmar",
+    "--export-wmar-json", "--import-wmar-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",