Add multi api

[MoDarK-MK]

Added interactive input for multiple API keys if none are set in the environment.

Stored all keys in a new environment variable LLM_API_KEYS (comma-separated).

The first key is also stored in LLM_API_KEY for backward compatibility.

Updated warm_up_llm() to try each API key in sequence until one succeeds.

Ensured no core logic or functionality of the original program was altered.