fix: prevent UI freeze after saving signed log entries

Cache plaintext list metadata on entry save so the journal list avoids
full decrypt per row, and batch sync pull writes with main-thread yields.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/utils/yieldToMain.ts

@@ -0,0 +1,24 @@
+/** Yield so long tasks can interleave with paint and input handling. */
+export function yieldToMain(): Promise<void> {
+  return new Promise((resolve) => {
+    setTimeout(resolve, 0)
+  })
+}
+
+/** Run an async handler over items in batches, yielding between batches. */
+export async function forEachInBatches<T>(
+  items: T[],
+  batchSize: number,
+  handler: (item: T) => Promise<void>
+): Promise<void> {
+  if (items.length === 0) return
+  const size = Math.max(1, batchSize)
+
+  for (let i = 0; i < items.length; i += size) {
+    if (i > 0) await yieldToMain()
+    const batch = items.slice(i, i + size)
+    for (const item of batch) {
+      await handler(item)
+    }
+  }
+}