COMMIT_EDITMSG

rspamd: Add LiteLLM GPT integration

- **modules/services/rspamd.nix**:  
  - Define a new SOPS secret `litellm-vulcan-lan` owned by the `rspamd` user,
    ensuring the secret is re‑loaded when the service restarts.
  - Extend `serviceConfig.LoadCredential` to expose the LiteLLM API key to the
    daemon alongside the existing controller password.
  - Introduce a temporary “info” logging level for GPT debugging (previously
    “warning”).
  - Add a new `gpt.conf` override containing full LiteLLM proxy configuration
    (type, URL, model, parameters, timeout, prompt, autolearn, reason header,
    and placeholder API key).
  - Add a post‑install script that reads the SOPS‑managed API key, writes it
    into `/var/lib/rspamd/override.d/gpt.conf`, and sets appropriate ownership
    and permissions.
  - Adjust comments and documentation throughout the file to reflect the new
    GPT/LLM integration flow.