refactor(providers): restructure provider creation with protocol-based configuration

- Move provider creation logic to factory_provider.go with protocol-based approach
- Add OpenAIProviderConfig with WebSearch support and embedded ProviderConfig
- Add maxTokensField to OpenAI-compatible provider for configurable token field
- Introduce new providers: Ollama, DeepSeek, GitHubCopilot, Antigravity, Qwen
- Remove redundant CreateProvider function from factory.go
- Add ThoughtSignature field to FunctionCall for tool response handling
- Remove duplicate Name field assignment in tool loop
- Update tests to reflect new provider configuration structure

pkg/providers/protocoltypes/types.go

@@ -9,8 +9,9 @@ type ToolCall struct {
 }
 
 type FunctionCall struct {
-	Name      string `json:"name"`
-	Arguments string `json:"arguments"`
+	Name             string `json:"name"`
+	Arguments        string `json:"arguments"`
+	ThoughtSignature string `json:"thought_signature,omitempty"`
 }
 
 type LLMResponse struct {