feat(config): add OCR URL configuration and improve image node handling

- Add VITE_OCR_URL environment variable with fallback URL construction
- Define IMAGE_NODE_TYPES constant to support 'image', 'image-block', and 'imageBlock' node types
- Add helper functions for safer image attribute access (getImageSrc, isImageNodeWithSrc, getImageLabel)
- Improve OCR error handling with HTTP status checking and error details
- Wrap OCR context in HTML comments to prevent prompt injection issues
- Update MilkdownEditor to use centralized OCR_URL configuration

src/utils/config.js

@@ -1,2 +1,18 @@
 export const DEBUG = import.meta.env.DEV
 export const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:8000/v1/completions'
+
+const buildDefaultOcrUrl = (apiUrl) => {
+  if (typeof window === 'undefined') {
+    return 'http://localhost:8000/v1/ocr'
+  }
+
+  try {
+    const url = new URL(apiUrl, window.location.origin)
+    url.pathname = '/v1/ocr'
+    return url.toString()
+  } catch {
+    return 'http://localhost:8000/v1/ocr'
+  }
+}
+
+export const OCR_URL = import.meta.env.VITE_OCR_URL || buildDefaultOcrUrl(API_URL)