Use API_KEY_COMFY_ORG env var for server-side API key in _helpers.py

### Feature Idea

Hey,

For most AI provider modules (openai, replicate etc), API keys are typically provided via environment variables rather than passed from the frontend. This approach makes deployments cleaner, simplifies configuration, and aligns ComfyUI with common practices.

**File:** `comfy_api_nodes/util/_helpers.py`

**Proposed change:**

* Check for `API_KEY_COMFY_ORG` in the environment first.
* Use it as the `X-API-KEY` header if present.
* Fall back to `node_cls.hidden` only if the env var is missing.

**Example implementation:**

```python
import os

def get_auth_header(node_cls):
env_api_key = os.getenv("API_KEY_COMFY_ORG")

if env_api_key:
return {"X-API-KEY": env_api_key}

if node_cls.hidden.auth_token_comfy_org:
return {"Authorization": f"Bearer {node_cls.hidden.auth_token_comfy_org}"}

if node_cls.hidden.api_key_comfy_org:
return {"X-API-KEY": node_cls.hidden.api_key_comfy_org}

return {}
```

This preserves self-hosted workflows while providing a standard environment-variable method for API keys, consistent with other AI provider modules. Unless I missed some other risk doing this?

Cheers,
Joe

### Existing Solutions

_No response_

### Other

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