refactor: split classroomController.js into 7 domain files (phase 2 of 2)

1618-line monolith split into:
  classroom/_shared.js     — GUEST_EVENTS, emitToSession, hasAccess, canDraw
  classroom/sessions.js    — lifecycle + guest tokens (12 functions)
  classroom/strokes.js     — CRUD + cursor + preview (7 functions)
  classroom/pages.js       — page CRUD + theme (8 functions)
  classroom/chat.js        — messages, reactions, attachments, export (7 functions)
  classroom/permissions.js — draw, hand, mute, screen, attendance (11 functions)
  classroom/sim.js         — simulation relay (5 functions)
  classroom/admin.js       — history, notes, templates, admin views (14 functions)

classroomController.js is now a 9-line re-export facade.
routes/classroom.js unchanged. All 65 exports verified. Tests pass.

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

backend/src/controllers/classroom/sim.js

@@ -0,0 +1,73 @@
+'use strict';
+const db = require('../../db/db');
+const { emitToSession } = require('./_shared');
+
+function simOpen(req, res) {
+  const sessionId = Number(req.params.id);
+  const session   = db.prepare(`SELECT * FROM classroom_sessions WHERE id=? AND status='active'`).get(sessionId);
+  if (!session) return res.status(404).json({ error: 'Сессия не активна' });
+  if (session.teacher_id !== req.user.id && req.user.role !== 'admin')
+    return res.status(403).json({ error: 'Нет доступа' });
+
+  const { simId, title } = req.body;
+  if (!simId || typeof simId !== 'string' || !/^[a-z0-9_-]{1,40}$/.test(simId))
+    return res.status(400).json({ error: 'Неверный simId' });
+
+  emitToSession(sessionId, { type: 'classroom_sim_open', sessionId, simId, title: (title || simId).slice(0, 80) });
+  res.json({ ok: true });
+}
+
+function simState(req, res) {
+  const sessionId = Number(req.params.id);
+  const session   = db.prepare(`SELECT * FROM classroom_sessions WHERE id=? AND status='active'`).get(sessionId);
+  if (!session) return res.status(404).json({ error: 'Сессия не активна' });
+  if (session.teacher_id !== req.user.id && req.user.role !== 'admin')
+    return res.status(403).json({ error: 'Нет доступа' });
+
+  const { state } = req.body;
+  if (!state || typeof state !== 'object') return res.status(400).json({ error: 'Нет state' });
+  const stateStr = JSON.stringify(state);
+  if (stateStr.length > 64_000) return res.status(413).json({ error: 'State слишком большой' });
+
+  emitToSession(sessionId, { type: 'classroom_sim_state', sessionId, state });
+  res.json({ ok: true });
+}
+
+function simMode(req, res) {
+  const sessionId = Number(req.params.id);
+  const session   = db.prepare(`SELECT * FROM classroom_sessions WHERE id=? AND status='active'`).get(sessionId);
+  if (!session) return res.status(404).json({ error: 'Сессия не активна' });
+  if (session.teacher_id !== req.user.id && req.user.role !== 'admin')
+    return res.status(403).json({ error: 'Нет доступа' });
+
+  const { mode } = req.body;
+  if (mode !== 'demo' && mode !== 'free') return res.status(400).json({ error: 'mode must be demo|free' });
+
+  emitToSession(sessionId, { type: 'classroom_sim_mode', sessionId, mode });
+  res.json({ ok: true });
+}
+
+function simAnnotate(req, res) {
+  const sessionId = Number(req.params.id);
+  const session   = db.prepare(`SELECT * FROM classroom_sessions WHERE id=? AND status='active'`).get(sessionId);
+  if (!session) return res.status(404).json({ error: 'Сессия не активна' });
+  if (session.teacher_id !== req.user.id && req.user.role !== 'admin')
+    return res.status(403).json({ error: 'Нет доступа' });
+
+  const { active } = req.body;
+  emitToSession(sessionId, { type: 'classroom_sim_annotate', sessionId, active: !!active });
+  res.json({ ok: true });
+}
+
+function simClose(req, res) {
+  const sessionId = Number(req.params.id);
+  const session   = db.prepare(`SELECT * FROM classroom_sessions WHERE id=? AND status='active'`).get(sessionId);
+  if (!session) return res.status(404).json({ error: 'Сессия не активна' });
+  if (session.teacher_id !== req.user.id && req.user.role !== 'admin')
+    return res.status(403).json({ error: 'Нет доступа' });
+
+  emitToSession(sessionId, { type: 'classroom_sim_close', sessionId });
+  res.json({ ok: true });
+}
+
+module.exports = { simOpen, simState, simMode, simAnnotate, simClose };