refactor(editor): extract single-file --convert-* into cli_convert_single.cpp

Moves the five single-file format converters (--convert-m2,
--convert-wmo, --convert-dbc-json, --convert-json-dbc,
--convert-blp-png) out of two dedicated post-loop blocks in
main.cpp into a new cli_convert_single.{hpp,cpp} module. The
batch wrappers in cli_convert.cpp keep working — they shell
out to wowee_editor with these flags.

main.cpp shrinks by ~335 lines (10,979 → 10,644). The two
trailing for-loops were dead code after wiring the dispatcher
into the main loop, so they're gone too.

tools/editor/cli_convert_single.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <string>
+
+namespace wowee {
+namespace editor {
+namespace cli {
+
+// Dispatch the single-file format-conversion handlers. These are
+// the source-of-truth implementations; the batch wrappers in
+// cli_convert.cpp shell out to wowee_editor with these flags.
+//   --convert-m2          M2 → WOM (uses asset manager + dataPath)
+//   --convert-wmo         WMO → WOB (uses asset manager + dataPath)
+//   --convert-dbc-json    DBC → JSON sidecar
+//   --convert-json-dbc    JSON sidecar → binary DBC
+//   --convert-blp-png     BLP → PNG
+//
+// dataPath is mutated to "Data" if empty so the M2/WMO handlers
+// have a default location to look in.
+//
+// Returns true if matched; outRc holds the exit code.
+bool handleConvertSingle(int& i, int argc, char** argv,
+                         std::string& dataPath, int& outRc);
+
+} // namespace cli
+} // namespace editor
+} // namespace wowee