Add SIM/LIVE switch with API keys saved to .env and OKX live executor.

Enable settings UI for mode/keys, gate strategy start when LIVE is not ready, and stop PM2 from forcing MODE=SIM.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/main.py

@@ -45,8 +45,9 @@ async def lifespan(app: FastAPI):
     try:
         await session.start()
         logger.info(
-            "exchange=%s strategy session started (SIM)",
+            "exchange=%s strategy session started mode=%s",
             settings.exchange,
+            "SIM" if get_settings().is_sim else "LIVE",
         )
     except Exception:
         logger.exception("strategy session failed to start")