feat(copilot): enhance OCR handling with inline tags and document serializer

- Replace HTML comment OCR metadata with inline `<OCR:...>` tags
- Implement serializer-based markdown conversion for prefix/suffix content
- Add extractTextFromOCR utility function for text extraction
- Enable Table, Diagram, and ListCheck features in MilkdownEditor
- Add periodic debug logging for document state analysis

src/utils/ocrCache.js

@@ -43,3 +43,11 @@ export function checkSizeLimit(docTextSize, imageFilenames) {
 }
 
 export const OCR_SIZE_LIMIT = SIZE_LIMIT
+
+export function extractTextFromOCR(ocrText, maxLen = 100) {
+  if (!ocrText) return ''
+  const match = ocrText.match(/TEXT:\s*([\s\S]*?)(?:KEY_DETAILS|LANGUAGE|SUMMARY|$)/i)
+  let text = match ? match[1].trim() : ocrText.trim()
+  if (text.toLowerCase() === '(none)') return ''
+  return text.length > maxLen ? text.substring(0, maxLen) + '...' : text
+}