refactor(editor): extract batch convert handlers into cli_convert.cpp

Moves the four bulk format-conversion handlers out of main.cpp:
  --convert-m2-batch    (M2 → WOM)
  --convert-wmo-batch   (WMO → WOB)
  --convert-blp-batch   (BLP → PNG)
  --convert-dbc-batch   (DBC → JSON)

These all share the same pattern: walk srcDir recursively for
files of the input extension and fan out to the single-file
--convert-* counterpart via subprocess (preserving the existing
per-file logic as the source of truth, no duplication).

Single-file converters (--convert-m2, --convert-wmo, etc.) and
the --migrate-* meta-commands still live in main.cpp; they're
in dedicated argv-rescan loops that need a different extraction
approach.

main.cpp drops 18,396 → 18,198 lines (-198). Behavior verified
by re-running --convert-blp-batch with a missing directory and
confirming the same error message.

tools/editor/cli_convert.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+namespace wowee {
+namespace editor {
+namespace cli {
+
+// Dispatch the batch format-conversion handlers:
+//   --convert-m2-batch    (M2 → WOM)
+//   --convert-wmo-batch   (WMO → WOB)
+//   --convert-blp-batch   (BLP → PNG)
+//   --convert-dbc-batch   (DBC → JSON)
+//
+// Each fans out to its single-file --convert-* counterpart via
+// subprocess so the existing per-file logic stays the source of
+// truth.
+//
+// Returns true if matched; outRc holds the exit code.
+bool handleConvert(int& i, int argc, char** argv, int& outRc);
+
+} // namespace cli
+} // namespace editor
+} // namespace wowee