Add student birthday tracking with celebration banners and admin notification; v1.1.31

- Admin can set birthday (month/day) per student in Study Users panel
- Summer birthdays (Jun–Aug) prompt admin to set an alternate school-year date
- 🎂 badge on student card header during birthday week
- Dismissible happy birthday banner shown to student on their study hub
- Admin receives email notification on the celebration day, once per year

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "1.1.30",
+  "version": "1.1.31",
   "type": "module",
   "scripts": {
     "dev": "vite",