T11: External adapters (Newgrounds, save) and secrets hygiene #24

Parent

Restructure spec: #13 (RESTRUCTURE_PLAN.md)

What to build

A Newgrounds adapter wrapping the ngio call path behind a game-shaped interface (post score, log event) with keys moved out of source into config/environment; a save adapter serializing AppState to user storage. Gameplay never touches the third-party path or its embedded secrets directly.

Acceptance criteria

• Score and log calls route through the adapter; game code depends only on its interface
• Keys resolve from config/environment, not from source
• AppState serialization round-trips verified in tests

Blocked by

• T3 AppSession composition root and AppState (T3: AppSession composition root and AppState #16)