feat(editor): add WKBD JSON round-trip (export/import sidecar)

Closes the JSON round-trip gap on the keybinding catalog
format shipped last batch. --export-wkbd-json emits all 7
scalar fields plus a dual int + name form for category (9
values) so hand-edits can use either representation.
--import-wkbd-json defaults isUserOverridable to 1 when
omitted (matches typical case for game-action bindings;
hardcoded engine bindings must explicitly set it to 0).
Verified byte-identical round-trip on all three preset
emitters (starter / movement with primary+alt keys / UI
panels). 798 documented CLI flags.

tools/editor/cli_arg_required.cpp

@@ -168,6 +168,7 @@ const char* const kArgRequired[] = {
     "--export-wsmc-json", "--import-wsmc-json",
     "--gen-kbd", "--gen-kbd-movement", "--gen-kbd-ui",
     "--info-wkbd", "--validate-wkbd",
+    "--export-wkbd-json", "--import-wkbd-json",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",