Discussion only open while a study is active; v2.11.1

- Community posts, replies, likes and lesson comments are refused (403) for finished and planned studies
- Reading a closed study's community/comments returns an empty list with closed:true
- Discussion hub lists only active studies; community page shows a closed notice
- Lesson page hides Lesson Discussion, 'Discuss this lesson' and 'Go to Community' for inactive studies; Community buttons hidden on study/dashboard pages
- Tests for isStudyDiscussionOpen

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.11.0",
+  "version": "2.11.1",
   "type": "module",
   "scripts": {
     "dev": "vite",