Add Hugging Face as a chat provider

Lets users with an existing Hugging Face account chat through HF's
Inference Providers router without signing up for another provider.
Model IDs are namespaced hf:org/model-name to avoid inferProvider's
OpenRouter "/" heuristic misrouting them; curated model list plus a
"Custom Model ID…" entry point stand in for HF's lack of a catalog/
pricing API.

oAI/Models/Settings.swift

@@ -57,10 +57,12 @@ struct Settings: Codable {
         case openai
         case ollama
         case appleOnDevice = "apple_on_device"
+        case huggingface
 
         var displayName: String {
             switch self {
             case .appleOnDevice: return "Apple Intelligence"
+            case .huggingface: return "Hugging Face"
             default: return rawValue.capitalized
             }
         }
@@ -72,6 +74,7 @@ struct Settings: Codable {
             case .openai: return "sparkles"
             case .ollama: return "server.rack"
             case .appleOnDevice: return "apple.logo"
+            case .huggingface: return "face.smiling"
             }
         }
     }