Improve media display and sorting for new posts

Optimized the "Nouvelle publication" media grid by limiting displayed items to 12, removing infinite scroll, implementing `useMemo` for cache safety, and adding conditional rendering for videos using `<video>` tags with `preload="metadata"`. Also fixed mobile calendar list sorting and added a visual separator for past dates.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ae4037a0-2a6f-4530-9bac-79b543286bda
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 19e08b6a-3862-4ea2-80f3-5c7b70ea15b1
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/397bca8c-984f-43ff-841a-10897aeb8140/ae4037a0-2a6f-4530-9bac-79b543286bda/YZ4cngz

replit.md

@@ -11,6 +11,7 @@ Preferred communication style: Simple, everyday language.
 ## Recent Changes
 
 ### November 5, 2025
+- **New Post Media Grid Optimization**: Optimized the "Nouvelle publication" media grid for better performance and usability. Changes: (1) Limited display to 12 most recent media items sorted by createdAt descending, (2) Removed infinite scroll functionality, (3) Implemented useMemo with spread copy to prevent React Query cache mutation during sorting, (4) Added conditional rendering for videos using `<video>` elements with `preload="metadata"` instead of broken `<img>` tags to display proper video thumbnails. This ensures faster page load, prevents cache corruption, and provides visual previews for both images and videos.
 - **Mobile Calendar Visual Separator**: Added visual separator between future and past dates in mobile calendar list view. A horizontal divider with centered text "PUBLICATIONS PASSÉES" now appears before the first past date when both future/today and past dates exist. The separator uses gray horizontal lines on both sides of uppercase text, providing clear visual distinction between upcoming posts and past posts. The separator only appears when transitioning from future to past dates - it does not show when only past or only future dates exist.
 - **Mobile Calendar List Sorting Fix**: Fixed illogical date ordering in mobile calendar list view. Problem: After displaying today's date first, remaining dates were sorted using simple localeCompare, mixing past and future dates together. Solution: Implemented intelligent chronological sorting in `calendar-list-view.tsx` with three-tier logic: (1) Today's date always appears first, (2) Future dates display in ascending chronological order (soonest first), (3) Past dates appear last in descending order (most recent first). The sorting uses ISO date string comparison (yyyy-MM-dd) which preserves chronological order. This provides intuitive navigation where users see today, then upcoming posts in order, then recent past posts.