Family devices: shared-screen family board with a who-is-this profile picker

- Admin can make a screen a family device; it opens on a family board
- Name tiles with KID labels; kids tap, others enter a PIN (lockout after 5 wrong tries)
- Name label with Switch user, auto-return to the board after 5 idle minutes
- Short 30-minute sessions on family devices
- Settings section for PIN and turning a device on or off
- Test, README and roadmap updated

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

docs/v2-roadmap.md

@@ -52,6 +52,7 @@ Not planned: voice and video calls, stories, usernames and phone-number lookup,
 ## 3. Kids and safety
 - [x] **Kid profiles (M):** tabs limited per child, content filters (the Smashwords-style filter, Store, podcasts and music in a clean mode), screen-time limits **Done: child accounts get a clean Store, podcasts and daily time limit and bedtime (kidlimits.js); tabs per child already existed.**
 - [ ] **Approvals (S):** a child asks to add a book, app or extension and a parent approves
+- [x] **Family device and profile picker (M):** a shared screen opens on the family board; kids tap their name, everyone else enters a PIN; it returns to the board when idle **Done: board.js, devices.js**
 - [ ] **Simple mode (S):** a big-button layout with few tabs for young kids or grandparents
 
 ## 4. Everyday convenience