Redesign community section with social media feed UX; v1.2.6

- Twitter/X-style post cards: avatar thread line, author + relative timestamp
- Heart like button with optimistic toggle and like count per post
- Comment button with reply count; inline threaded replies always visible
- Compose card with user avatar, borderless textarea, pill Post button
- Horizontal scrollable lesson filter chips (All + per-lesson)
- New POST /api/study-community/posts/:postId/like endpoint (toggle)
- GET community posts now returns likedByMe + likeCount per post
- sanitizeStudyCommunityPosts preserves likedBy array on disk
- Relative timestamps (just now, Xm ago, Xh ago, Xd ago, then date)
- UserAvatar helper renders img or initials fallback consistently

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "1.2.5",
+  "version": "1.2.6",
   "type": "module",
   "scripts": {
     "dev": "vite",