feat(editor): Find Valid Tile button, improved ADT loading workflow

- "Find Valid Tile" button in Load dialog: auto-scans manifest for the
  first available ADT tile of the selected map (checks center range
  25-45 first for open world, then full 0-63 for dungeons)
- Fixes "wrong coords" issue — dungeons use different tile coords than
  open world maps, now auto-detected
- Map name lowercased for manifest lookup consistency
- Tile check shows green "Tile found" or red "Tile not found" indicator

tools/editor/asset_browser.hpp

@@ -28,6 +28,7 @@ public:
     const std::vector<std::string>& getWMODirectories() const { return wmoDirs_; }
 
     const std::vector<std::string>& getMapNames() const { return mapNames_; }
+    std::vector<std::pair<int,int>> getMapTiles(const std::string& mapName) const;
 
     bool isInitialized() const { return initialized_; }