fix: use DATABASE_FILE env var consistently and update Dockerfile

Dockerfile

@@ -42,8 +42,8 @@ RUN apt-get update && apt-get install -y ca-certificates sqlite3 && rm -rf /var/
 # Create data directory for sqlite
 RUN mkdir -p /app/data
 
-# Set DB_PATH to use the persistent volume
-ENV DB_PATH=/app/data/mal.db
+# Set DATABASE_FILE to use the persistent volume
+ENV DATABASE_FILE=/app/data/mal.db
 
 COPY --from=builder /app/main_server .
 COPY --from=builder /app/templates ./templates