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_diff_headers.hpp

@@ -0,0 +1,11 @@
+#pragma once
+
+namespace wowee {
+namespace editor {
+namespace cli {
+
+bool handleDiffHeaders(int& i, int argc, char** argv, int& outRc);
+
+} // namespace cli
+} // namespace editor
+} // namespace wowee