Add translation cache for faster repeated translations (5000 entry LRU cache with hit rate tracking)

main.py

@@ -21,6 +21,7 @@ import time
 from config import config
 from translators import excel_translator, word_translator, pptx_translator
 from utils import file_handler, handle_translation_error, DocumentProcessingError
+from services.translation_service import _translation_cache
 
 # Import auth routes
 from routes.auth_routes import router as auth_router
@@ -228,7 +229,8 @@ async def health_check():
             "rate_limits": {
                 "requests_per_minute": rate_limit_config.requests_per_minute,
                 "translations_per_minute": rate_limit_config.translations_per_minute,
-            }
+            },
+            "translation_cache": _translation_cache.stats()
         }
     )