Add RuntimeTool model and enhance AssistantConfig for tool management

- Introduce a new `RuntimeTool` model to encapsulate tool data for runtime sessions, including attributes like `id`, `name`, `function_name`, `type`, and `description`.
- Update the `AssistantConfig` model to include a list of reusable tools, allowing for better management of tools within assistant configurations.
- Modify the `config_resolver` service to fetch and resolve tools associated with assistants, ensuring they are available during runtime.
- Refactor tool-related CRUD operations in the `tools` route to support the new runtime execution model, enhancing the overall tool management system.
- Update documentation and comments to reflect changes in tool execution and configuration handling, improving clarity for future development.

backend/db/models.py

@@ -148,7 +148,7 @@ class AssistantModelBinding(Base):
 
 
 class Tool(Base):
-    """Reusable LLM tool definition. Runtime execution is added separately."""
+    """Reusable LLM tool definition; supported types are executed at runtime."""
 
     __tablename__ = "tools"