docs: add Hugging Face provider to all documentation pages

- quickstart.md: add to provider table
- configuration.md: add to provider table, add dedicated section with
  usage examples, config.yaml snippet, routing suffixes, and token info;
  also fix pre-existing duplicate Alibaba Cloud entry
- environment-variables.md: add HF_TOKEN + HF_BASE_URL, add huggingface
  to HERMES_INFERENCE_PROVIDER values
- fallback-providers.md: add to supported providers table and
  auto-detection chain

website/docs/user-guide/features/fallback-providers.md

@@ -44,6 +44,7 @@ Both `provider` and `model` are **required**. If either is missing, the fallback
 | MiniMax | `minimax` | `MINIMAX_API_KEY` |
 | MiniMax (China) | `minimax-cn` | `MINIMAX_CN_API_KEY` |
 | Kilo Code | `kilocode` | `KILOCODE_API_KEY` |
+| Hugging Face | `huggingface` | `HF_TOKEN` |
 | Custom endpoint | `custom` | `base_url` + `api_key_env` (see below) |
 
 ### Custom Endpoint Fallback
@@ -161,7 +162,7 @@ When a task's provider is set to `"auto"` (the default), Hermes tries providers
 
 ```text
 OpenRouter → Nous Portal → Custom endpoint → Codex OAuth →
-API-key providers (z.ai, Kimi, MiniMax, Anthropic) → give up
+API-key providers (z.ai, Kimi, MiniMax, Hugging Face, Anthropic) → give up
 ```
 
 **For vision tasks:**