Parent controls for children, name-tile sign-in, restricted Learn search, simple mode

- Sign-in page shows name tiles on remembered devices; tap a name, then PIN or passkey
- Music and Movies are separate on the server; Plex can be locked to a child's managed profile
- Activity log, weekly summary and alerts to parents; per-area and weekend limits
- Requests from children (Ask button) answered in Settings; bonus screen time from rewards
- Restricted Learn search (Simple English Wikipedia, blocked words) replaces web search for children
- Simple mode (big-button home) for young children or grandparents
- Child usage kept in memory instead of read from disk on every request
- Tests and README updated

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

public/boot.js

@@ -18,7 +18,7 @@
   setInterval(checkForUpdate, 10 * 60e3);
   await loadMe();
   await loadSettings();
-  sgStart(); if (typeof chStart === 'function') chStart(); if (typeof kidStart === 'function') kidStart(); if (typeof devStart === 'function') devStart();
+  sgStart(); if (typeof chStart === 'function') chStart(); if (typeof kidStart === 'function') kidStart(); if (typeof devStart === 'function') devStart(); if (typeof simpleStart === 'function') simpleStart();
   addEventListener('hashchange', route);
   restorePlayer();
   route();