feat(editor): in-editor "Random Populate" menu mirrors CLI

Adds EditorApp::randomPopulateZone(creatureCount, objectCount, seed)
and a Generate-menu submenu with sliders for both counts plus a
seed input. Same logic and bestiary as the --random-populate-zone
CLI: 12 creature templates with level jitter, 5 placeholder WMO
prop types with randomized rotation/scale.

Spawns are placed within the loaded tile's world bbox, marked
dirty + auto-save pending so the populated content persists across
restarts.

The CLI command remains for CI / scripting / batch workflows; the
menu serves designers who want to populate from the GUI without
context-switching to a terminal.

Same-seed reproducibility: a hover hint reminds the user that the
seed determines the output deterministically.

tools/editor/editor_app.hpp

@@ -98,6 +98,10 @@ public:
     int batchConvertAssets(const std::string& dataDir);
     void clearAllObjects();
     void generateCompleteZone();
+    // Drop N random creatures + M random objects within the loaded
+    // tile's world bbox. Mirrors the --random-populate-zone CLI
+    // command so users can do bulk population from inside the editor.
+    void randomPopulateZone(int creatureCount, int objectCount, uint32_t seed);
     void centerOnTerrain();
 
     // Multi-tile support