feat(memory): add grounded REM backfill lane (#63273)

Merged via squash.

Prepared head SHA: 4450f25485
Co-authored-by: mbelinky <132747814+mbelinky@users.noreply.github.com>
Co-authored-by: mbelinky <132747814+mbelinky@users.noreply.github.com>
Reviewed-by: @mbelinky

extensions/memory-core/api.ts

@@ -4,3 +4,8 @@ export type {
   MemoryProviderStatus,
   MemorySyncProgressUpdate,
 } from "openclaw/plugin-sdk/memory-core-host-engine-storage";
+export {
+  removeBackfillDiaryEntries,
+  writeBackfillDiaryEntries,
+} from "./src/dreaming-narrative.js";
+export { previewGroundedRemMarkdown } from "./src/rem-evidence.js";