Redesign study Notes, Reflection questions and Community pages; v2.12.0

- Notes: two-pane reader with searchable lesson list and snippets, track chips, friendlier empty states
- Reflection questions: numbered question cards, answered progress bar, unsaved-changes status, sticky save bar, share-to-discussion only when discussion is open
- Community: compact header, lesson browser sidebar with post counts (select on mobile), guidelines card, card-style posts

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.11.2",
+  "version": "2.12.0",
   "type": "module",
   "scripts": {
     "dev": "vite",