Add bottle size, bourbon list modal, and stat improvements

- Add bottle_size field to User model and UserResponse/UserUpdate schemas
- Settings modal includes bottle size input (shots capacity)
- Community bottles and My Bottle page show fill bar based on bottle size
- Community bottle cards are clickable — opens searchable bourbon list modal
- Add total_shots_added stat to replace duplicate net volume on dashboard
- Reorder dashboard stats: Bourbons Added, Total Poured In, Shots Remaining, Est. Proof
- Theme-matched custom scrollbar (amber on dark)

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

backend/app/routers/users.py

@@ -24,6 +24,7 @@ async def update_me(
         current_user.display_name = body.display_name
     if body.timezone is not None:
         current_user.timezone = body.timezone
+    current_user.bottle_size = body.bottle_size
 
     db.add(current_user)
     await db.commit()