refactor(ocr): 重构OCR配置结构以支持默认提供者

将内置OCR提供者数组重构为单独定义的常量，并添加默认OCR提供者映射。这提高了代码的可维护性并支持未来扩展。

src/renderer/src/config/ocr.ts

@@ -1,11 +1,15 @@
-import { BuiltinOcrProvider } from '@renderer/types/ocr'
+import { BuiltinOcrProvider, ImageOcrProvider, OcrProviderCapability } from '@renderer/types/ocr'
 
-export const BUILTIN_OCR_PROVIDERS: BuiltinOcrProvider[] = [
-  {
-    id: 'tesseract',
-    name: 'Tesseract',
-    capabilities: {
-      image: true
-    }
+const tesseract: BuiltinOcrProvider & ImageOcrProvider = {
+  id: 'tesseract',
+  name: 'Tesseract',
+  capabilities: {
+    image: true
   }
-] as const
+} as const
+
+export const BUILTIN_OCR_PROVIDERS: BuiltinOcrProvider[] = [tesseract] as const
+
+export const DEFAULT_OCR_PROVIDER: Record<OcrProviderCapability, BuiltinOcrProvider> = {
+  image: tesseract
+} as const