fix: тема доски синхронизируется между учителем и учениками в реальном времени

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

frontend/classroom.html

@@ -3160,6 +3160,7 @@
   let _me = null;
   let _session = null;
   let _sessionId = null;
+  let _sessionBoardTheme = null; // pending theme from session data, applied in initWhiteboard
   let _sseHandle = null;
   let _participants = {};   // userId -> {name, micMuted}
   let _raisedHands  = {};   // userId -> userName
@@ -3554,6 +3555,12 @@
         if (sel) sel.value = data.template;
         wbUpdateThumbnail(_wbCurrentPage);
       }
+    } else if (data.type === 'classroom_board_theme') {
+      if (_sessionId == data.sessionId && _wb) {
+        _wb.setBoardTheme(data.theme);
+        const sel = document.getElementById('wb-theme-select');
+        if (sel) sel.value = data.theme;
+      }
     } else if (data.type === 'classroom_hand_raised') {
       if (_sessionId == data.sessionId) onHandRaised(data.userId, data.userName);
     } else if (data.type === 'classroom_hand_lowered') {
@@ -3981,6 +3988,8 @@
     // page state
     _wbCurrentPage = session.current_page || 1;
     _totalPages    = session.pageCount    || 1;
+    // Remember board theme from session — will be applied in initWhiteboard
+    if (session.board_theme) _sessionBoardTheme = session.board_theme;
     _raisedHands   = {};
     _handRaised    = false;
     _followTeacher = true;
@@ -4069,8 +4078,12 @@
       stylusMultiplier: _prefs.stylusMultiplier,
     });
 
-    // Sync board theme selector to whiteboard default
-    { const sel = document.getElementById('wb-theme-select'); if (sel) sel.value = 'chalkboard'; }
+    // Apply session board theme (set by teacher, synced for all participants)
+    if (_sessionBoardTheme && _sessionBoardTheme !== 'chalkboard') {
+      _wb.setBoardTheme(_sessionBoardTheme);
+    }
+    { const sel = document.getElementById('wb-theme-select'); if (sel) sel.value = _sessionBoardTheme || 'chalkboard'; }
+    _sessionBoardTheme = null; // consumed
 
     // Apply saved whiteboard defaults from user preferences
     if (canEdit && LS.prefs) {
@@ -5508,10 +5521,13 @@
   function wbSetBoardTheme(theme) {
     if (!_wb) return;
     _wb.setBoardTheme(theme);
-    // Update selector if called programmatically
     const sel = document.getElementById('wb-theme-select');
     if (sel) sel.value = theme;
     if (LS.prefs) LS.prefs.set('wb.theme', theme);
+    // Broadcast to students if in active session
+    if (_sessionId) {
+      LS.patch(`/api/classroom/${_sessionId}/board-theme`, { theme }).catch(() => {});
+    }
   }
 
   /* ── Page context menu ── */