feat: add IsUnset method to LLMProvider

Introduced a new method to check if an LLM provider is considered unset:
- Added Unset field to LLMProvider struct
- Implemented IsUnset() method with logic to validate provider configuration
- Handles special cases for different provider types (azure-openai, openai-compatible)
- Checks for empty API key, missing models, and provider-specific configuration requirements

core/models/models/llm_provider.go

@@ -11,4 +11,21 @@ type LLMProvider struct {
 	ApiBaseUrl             string   `json:"api_base_url" bson:"api_base_url"` // API base URL for the provider
 	ApiVersion             string   `json:"api_version" bson:"api_version"`   // API version for the provider
 	Models                 []string `json:"models" bson:"models"`             // Models supported by this provider
+	Unset                  bool     `json:"unset" bson:"-"`                   // Whether the provider is unset
+}
+
+func (p *LLMProvider) IsUnset() bool {
+	if p.ApiKey == "" {
+		return true
+	}
+	if len(p.Models) == 0 {
+		return true
+	}
+	switch p.Key {
+	case "azure-openai":
+		return p.ApiBaseUrl == "" && p.ApiVersion == ""
+	case "openai-compatible":
+		return p.ApiBaseUrl == ""
+	}
+	return false
 }