feat: WebSocket real-time + rAF render gate + guest board + screen picker

Classroom performance:
- WebSocket server (ws-server.js) for low-latency cursor & stroke preview
  Replaces HTTP POST per event → eliminates per-message auth overhead
  Session member cache (30s TTL) avoids SQLite query per WS message
  Fallback to HTTP POST when WS not connected
- Cursor throttle reduced 100ms → 33ms (~30fps)
- Stroke preview throttle reduced 50ms → 20ms
- whiteboard.js: render() is now rAF-gated (_doRender/_rafPending)
  Multiple render() calls within one frame collapse into one repaint
  document.hidden check — zero CPU when tab is in background
  visibilitychange listener restores canvas on tab focus

Guest board:
- guestClassroom.js route: public token-based read-only access
- guest-board.html: name entry + read-only whiteboard + SSE
- SSE: addGuestClient/removeGuestClient/emitToGuests

Screen share picker:
- Discord-style modal with tab switching (screen/window/tab)
- Live video preview before confirming share
- useExistingScreenStream() in ClassroomRTC

Fullscreen exit overlay:
- #cr-fs-exit-overlay button inside cr-board-wrap
- Visible only via CSS :fullscreen selector (touchpad users)

File sharing from library:
- Teacher picks file from library, sends as styled card in chat
- crDownloadLibraryFile() fetches with Bearer auth

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

backend/src/routes/classroom.js

@@ -30,9 +30,16 @@ const auth    = [authMiddleware];
 const chatLimiter = rateLimit({ windowMs: 5_000, max: 5, message: 'Слишком много сообщений, подождите' });
 
 // Template library — MUST be before /:id to avoid shadowing
+router.get('/admin/active',               ...teacher, c.adminGetActiveSessions);
+router.get('/admin/sessions',             ...teacher, c.adminGetAllSessions);
+router.get('/admin/teachers-list',        ...teacher, c.adminGetTeachersList);
 router.get('/templates',                  ...teacher, c.getTemplates);
 router.delete('/templates/:tid',          ...teacher, c.deleteTemplate);
 
+// History — MUST be before /:id to avoid shadowing
+router.get('/my/history',                 ...auth,    c.getMyHistory);
+router.get('/class/:classId/history',     ...auth,    c.getClassHistory);
+
 // Session lifecycle
 router.post('/',                          ...teacher, c.createSession);
 router.get('/online-students',            ...teacher, c.getOnlineStudents);
@@ -65,9 +72,13 @@ router.patch('/:id/strokes/:strokeId',    ...auth,    c.updateStroke);
 router.post('/:id/stroke-preview',        ...auth,    c.previewStroke);
 
 // Multi-page
-router.post('/:id/pages',                 ...teacher, c.addPage);
-router.put('/:id/page',                   ...teacher, c.changePage);
-router.patch('/:id/page-template',        ...teacher, c.updatePageTemplate);
+router.get('/:id/pages',                          ...auth,    c.getPages);
+router.post('/:id/pages',                         ...teacher, c.addPage);
+router.put('/:id/page',                           ...teacher, c.changePage);
+router.patch('/:id/page-template',                ...teacher, c.updatePageTemplate);
+router.patch('/:id/pages/:pageNum/name',          ...teacher, c.renamePage);
+router.post('/:id/pages/:pageNum/duplicate',      ...teacher, c.duplicatePage);
+router.delete('/:id/pages/:pageNum',              ...teacher, c.deletePage);
 
 // Hand raise
 router.post('/:id/hand',                  ...auth,    c.raiseHand);
@@ -82,6 +93,12 @@ router.post('/:id/mute',                  ...teacher, c.mutePeer);
 router.post('/:id/screen',                ...teacher, c.screenStart);
 router.delete('/:id/screen',              ...teacher, c.screenStop);
 
+// Simulation: open/close/state/mode for all participants
+router.post('/:id/sim',                   ...teacher, c.simOpen);
+router.delete('/:id/sim',                 ...teacher, c.simClose);
+router.post('/:id/sim/state',             ...teacher, c.simState);
+router.post('/:id/sim/mode',              ...teacher, c.simMode);
+
 // Cursor broadcast (all participants)
 router.post('/:id/cursor',                ...auth,    c.broadcastCursor);
 
@@ -95,10 +112,21 @@ router.delete('/:id/allow-draw/:userId',  ...teacher, c.revokeDraw);
 // Session notes (per user)
 router.get('/:id/notes',                  ...auth,    c.getNotes);
 router.put('/:id/notes',                  ...auth,    c.saveNotes);
+router.get('/:id/notes/all',              ...teacher, c.getAllNotes);
+
+// Session summary & history detail
+router.get('/:id/summary',                ...auth,    c.getSessionSummary);
+router.get('/:id/chat/export',            ...teacher, c.exportChat);
+router.delete('/:id/history',             ...teacher, c.deleteHistorySession);
 
 // Save current session as template
 router.post('/:id/save-template',         ...teacher, c.saveTemplate);
 // Load template into current session
 router.post('/:id/load-template',         ...teacher, c.loadTemplate);
 
+// Guest token (generate/revoke/get)
+router.get('/:id/guest-token',            ...teacher, c.getGuestToken);
+router.post('/:id/guest-token',           ...teacher, c.generateGuestToken);
+router.delete('/:id/guest-token',         ...teacher, c.revokeGuestToken);
+
 module.exports = router;