- add new WordSage AI-powered word explanation tool

- update sidebar navigation to include WordSage link
- register WordSage in tools.json with appropriate metadata
- completely overhaul chess game with improved UI and functionality:
  - add move history with navigation
  - implement AI opponent with difficulty levels
  - add board flip functionality
  - track captured pieces
  - improve responsive design
- update sitemap.xml to include WordSage page

Author: TobiasMue91

data/tools.json

@@ -1175,5 +1175,16 @@
     "aiPowered": false,
     "featured": false,
     "date": "2025-03-13"
+  },
+  {
+    "id": "word_explainer",
+    "title": "WordSage",
+    "description": "AI word explanations customized for any educational level.",
+    "url": "tools/word_explainer.html",
+    "screenshot": "screenshots/screenshot_158.png",
+    "type": "tool",
+    "aiPowered": true,
+    "featured": false,
+    "date": "2025-03-16"
   }
 ]