feat: 更新模块文档，添加详细说明和使用示例

src/minenasai/llm/base.py

@@ -6,13 +6,17 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
+from collections.abc import AsyncIterator
 from dataclasses import dataclass, field
-from enum import Enum
-from typing import Any, AsyncIterator
+from enum import StrEnum
+from typing import Any
 
 
-class Provider(str, Enum):
-    """LLM 提供商"""
+class Provider(StrEnum):
+    """LLM 提供商
+
+    支持的 AI API 提供商枚举。
+    """
 
     ANTHROPIC = "anthropic"  # Claude
     OPENAI = "openai"  # GPT