feat(editor): add image insertion with OCR support and size limit handling

Add image button with dropdown menu for uploading local images or inserting from URL.
Integrate VLM-based OCR to extract text context from images and include in AI suggestions.
Implement document size limits to disable AI when exceeding threshold.
Refactor copilot plugin with per-view runtime state and OCR context injection.
Add OCR cache utility for managing image metadata.
Add code splitting configuration for optimized bundle size.

src/utils/ocrCache.js

@@ -0,0 +1,45 @@
+const SIZE_LIMIT = 64 * 1024
+
+const ocrCache = new Map()
+
+export function setOcrCache(filename, text) {
+  ocrCache.set(filename, text)
+}
+
+export function getOcrCache(filename) {
+  return ocrCache.get(filename) || ''
+}
+
+export function clearOcrCache(filename) {
+  ocrCache.delete(filename)
+}
+
+export function hasOcrCache(filename) {
+  return ocrCache.has(filename)
+}
+
+export function clearAllOcrCache() {
+  ocrCache.clear()
+}
+
+export function calculateOcrSize(imageFilenames) {
+  let total = 0
+  for (const name of imageFilenames) {
+    const text = ocrCache.get(name)
+    if (text) total += new Blob([text]).size
+  }
+  return total
+}
+
+export function checkSizeLimit(docTextSize, imageFilenames) {
+  const ocrSize = calculateOcrSize(imageFilenames)
+  const total = docTextSize + ocrSize
+  return {
+    size: total,
+    docSize: docTextSize,
+    ocrSize: ocrSize,
+    overLimit: total > SIZE_LIMIT
+  }
+}
+
+export const OCR_SIZE_LIMIT = SIZE_LIMIT