Fix: Raise exception when .env is left unchanged after copying .env.example

[shinchri]

Changes:

• Replace unnecessary f-string from 'llm/models.py' with regular string
• Check for unchanged value from copying .env.example (see below).

if not api_key into if not api_key or api_key == "your-anthropic-api-key"

[MC-intel]

This is a helpful fix, ensuring users don’t mistakenly run with an unchanged API key. Another approach could be prompting the user to enter their API key during setup if the key is missing or default. That way, it’s caught before execution. What do you think about adding a warning message in the logs as well?

[shinchri]

When you say logs, do you mean print messages in the file to actually say API key was left unchanged?