feature: 新增小说封面图片生成功能

backend/app/services/cover_providers/base_cover_provider.py

@@ -0,0 +1,32 @@
+"""封面图片 Provider 抽象基类"""
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Optional, TypedDict
+
+
+class CoverGenerationResult(TypedDict):
+    """封面生成结果"""
+
+    content: bytes
+    mime_type: str
+    file_extension: str
+    revised_prompt: Optional[str]
+    provider: str
+    model: str
+
+
+class BaseCoverProvider(ABC):
+    """封面图片 Provider 抽象基类"""
+
+    @abstractmethod
+    async def generate_cover(
+        self,
+        *,
+        prompt: str,
+        model: str,
+        width: int,
+        height: int,
+    ) -> CoverGenerationResult:
+        """生成封面图片"""
+        raise NotImplementedError