perf: enable fastPreview for legacy .json files and prioritize metadata lastUpdated for perfect sorting

Author: N1kky-wed

packages/cli/src/utils/sessionUtils.ts

@@ -360,10 +360,7 @@ export const getAllSessionFiles = async (
             const fallbackTimestamp = fileTimestamp ?? new Date().toISOString();
             const startTime = content.startTime || fallbackTimestamp;
 
-            const lastUpdated =
-              !options.includeFullContent && fileTimestamp
-                ? fileTimestamp
-                : content.lastUpdated || fallbackTimestamp;
+            const lastUpdated = content.lastUpdated || fallbackTimestamp;
 
             if (!content.hasUserOrAssistantMessage) {
               return { fileName: file, sessionInfo: null };