refactor: fix P0/P1/P2 security and performance issues

P0 fixes:
- CORS: replace wildcard methods/headers with configurable lists
- deps.py: remove unsafe global _warned_unset variable

P1 fixes:
- http_client: read default timeout from Settings
- bzzoiro: replace sync urllib with async httpx
- bzzoiro: normalize validation failures use warning level only
- db pool: read pool config from Settings (default 5+10)
- backtest: add asyncio.Semaphore(8) for concurrent execution
- predict/context_builder: add backtest parameter for cutoff buffer

P2 improvements:
- injuries: enforce int conversion for player_id/fixture_id
- injuries: use system temp dir for cache
- utils.py: extract shared actual_1x2/is_correct_1x2
- validation: downgrade 1x2 mismatch log to debug
- docker-compose: use env vars for all credentials
- .env.example: add POSTGRES_USER/PASSWORD/PORT, API_PORT

src/api/app.py

@@ -29,12 +29,14 @@ def create_app() -> FastAPI:
     )
 
     origins = [o.strip() for o in settings.CORS_ORIGINS.split(",") if o.strip()]
+    methods = [m.strip() for m in settings.CORS_METHODS.split(",") if m.strip()]
+    headers = [h.strip() for h in settings.CORS_HEADERS.split(",") if h.strip()]
     app.add_middleware(
         CORSMiddleware,
         allow_origins=origins,
         allow_credentials=True,
-        allow_methods=["*"],
-        allow_headers=["*"],
+        allow_methods=methods,
+        allow_headers=headers,
     )
 
     from src.api.routes.matches import router as matches_router