Add unified FEN/PGN import with auto-detection

- Create chessFormatDetector utility for automatic format detection
- Update StartScreen with textarea supporting both FEN and PGN input
- Add real-time format detection with visual feedback indicators
- Update translations for all 4 languages (EN, DE, FR, IT)
- Add markdown rendering for Tutor chat messages
- Add comprehensive tests for format detection (20 tests)
- Update game initialization to handle both FEN and PGN formats

This completes the fix/stale-analysis-data branch with:
- Fixed stale evaluation data in hint/best move requests
- Clarified AI's dual role (opponent + tutor) to prevent hint rejection
- Stored complete evaluation history (P0, P1, P2) for all moves
- Improved end-game analysis with better mistake detection
- Fixed duplicate analysis runs with useRef flag
- Added markdown rendering for formatted analysis output
- Added unified FEN/PGN import with auto-detection

package.json

@@ -19,6 +19,7 @@
     "react": "19.2.0",
     "react-chessboard": "^5.8.4",
     "react-dom": "19.2.0",
+    "react-markdown": "^10.1.0",
     "stockfish.js": "^10.0.2",
     "tailwind-merge": "^3.4.0"
   },
@@ -40,4 +41,4 @@
     "ts-node": "^10.9.2",
     "typescript": "^5"
   }
-}
+}