refactor: remediation plan Fase 0-4 completata

- Fase 0: env var allineate, SYSTEM_PROMPT deduplicato, .gitignore pulito
- Fase 1: GameContext isolato, ciclo DM unificato, provider thread-safe (contextvars)
- Fase 2: DB schema esteso (current_area_id, combat_state, character_items)
- Fase 3: thread-local connection pool + WAL + busy_timeout
- Fase 4: test suite (32 test, 100% pass)
- heuristic_fallback come parser di riserva (non secondo pilota)

src/web/server.py

@@ -12,7 +12,7 @@ from fastapi.staticfiles import StaticFiles
 from src.engine import db
 from src.engine.config import load_from_env
 from src.engine.dm import dm_cycle
-from src.engine.state_machine import GameContext
+from src.engine.game_context import GameContext
 
 log = logging.getLogger(__name__)