refactor(editor): extract 10 diff handlers into cli_diff.cpp

Moves the file-comparison handlers out of main.cpp into their
own translation unit:
  --diff-wcp        --diff-zone
  --diff-glb        --diff-wom
  --diff-wob        --diff-whm
  --diff-woc        --diff-jsondbc
  --diff-extract    --diff-checksum

main.cpp drops 15,653 → 14,732 lines (-921). One build error
during extraction (missing #include for NpcSpawner /
ObjectPlacer / QuestEditor used by --diff-zone) caught by
build and fixed.

tools/editor/cli_diff.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+namespace wowee {
+namespace editor {
+namespace cli {
+
+// Dispatch the diff handlers — each compares two files of the
+// same format and reports differences:
+//   --diff-wcp        --diff-zone
+//   --diff-glb        --diff-wom
+//   --diff-wob        --diff-whm
+//   --diff-woc        --diff-jsondbc
+//   --diff-extract    --diff-checksum
+//
+// Returns true if matched; outRc holds the exit code.
+bool handleDiff(int& i, int argc, char** argv, int& outRc);
+
+} // namespace cli
+} // namespace editor
+} // namespace wowee