feat(editor): add --diff-headers cross-file header comparison

Compares two .w* files at the standard catalog header level:
4-byte magic, version, catalog name, entry count, total file
bytes. Useful for confirming a JSON round-trip didn't drift,
checking whether two preset emissions produced equivalent
output, or quickly diagnosing when a content snapshot has
silently shifted (entry count up means content was added,
file bytes up but everything else same means entry payloads
got fatter).

Output uses = / ≠ markers per field so visual scanning is
fast. Three diagnostic summary cases: identical headers (and
same bytes — possibly byte-equal, run cmp(1) to confirm),
same shape but bytes differ (entry payloads diverged), and
different formats entirely (files are unrelated).

Returns exit 1 if any field differs, so the flag composes
into shell pipelines (`if diff-headers a.wcms b.wcms; then ...`).
World/asset formats stop after magic since their layouts
diverge from the standard catalog header.

Supports --json variant for tooling integration.

tools/editor/cli_arg_required.cpp

@@ -136,7 +136,7 @@ const char* const kArgRequired[] = {
     "--export-wliq-json", "--import-wliq-json",
     "--info-magic", "--summary-dir", "--rename-by-magic",
     "--bulk-rename-by-magic", "--touch-tree", "--tree-summary-md",
-    "--catalog-grep",
+    "--catalog-grep", "--diff-headers",
     "--gen-animations", "--gen-animations-combat", "--gen-animations-movement",
     "--info-wani", "--validate-wani",
     "--export-wani-json", "--import-wani-json",