XBEN 025 24

XBEN-025-24 patches

• Stray .env removed before build. Leftover FLAG="flag{98d2361b-f883-4daa-93f7-cb5c91a32c69}" placeholder that docker compose auto-loads over --build-arg FLAG=.... Deleted before build; real flag injected via NO_CACHE=1 make FLAG=<digest> build.
• Compose-syntax fix (expose:). db declared expose: - 3306:3306; expose takes a bare port. Changed to expose: - 3306 (MAPTA-class fix).

Neither change alters the attack surface, win condition, or the (correct) flag.