feat(extract): emit WOM and WOB side-files (M2/WMO → open formats)

Extends asset_extract with two more open-format emitters:
  --emit-wom  foo.m2 (+ foo00.skin) → foo.wom
  --emit-wob  foo.wmo (+ foo_NNN.wmo groups) → foo.wob
  --emit-open now also turns these on

Originals are preserved so private servers still load .m2/.wmo
through the manifest path; the wowee runtime/editor pick up the
.wom/.wob next to them via the existing open-format search rules.

Implementation:
- New WoweeModelLoader::fromM2Bytes(m2Data, skinData) shares the
  conversion body with fromM2(path, am) via a static helper
  (convertM2ToWom). Lets the extractor convert without standing
  up an AssetManager.
- fromM2(path, am) moved to a separate translation unit
  (wowee_model_fromm2.cpp) so asset_extract doesn't have to
  link the AssetManager dependency.
- WoweeBuildingLoader::fromWMO already takes a WMOModel directly,
  so emitWobFromWmo just needs to read root + group files and
  call save().
- Group sub-files (<base>_NNN.wmo) are skipped during the walk
  since they're merged into the root WMO.

tools/asset_extract/extractor.hpp

@@ -34,6 +34,8 @@ public:
         // private servers (AzerothCore/TrinityCore) read from.
         bool emitPng = false;          // BLP → PNG side-files
         bool emitJsonDbc = false;      // DBC → JSON side-files
+        bool emitWom = false;          // M2 (+skin) → WOM side-files
+        bool emitWob = false;          // WMO (+groups) → WOB side-files
     };
 
     struct Stats {