feat(trainer): ИИ-тренажёр — генераторы задач + SimExpr-верификатор, прогресс, фича-флаг

- движок _trainer_engine.js: instantiate/generateBatch/verifyRoot/checkStudentAnswer/exprToLatex
- 5 генераторов уравнений 7 класса (generators.js), приём «корень-вперёд» → целые ответы
- страница /trainer: KaTeX-рендер, чипы-темы, мгновенная проверка, подсказка/решение, авто-выбор навыка
- прогресс practice_progress (мигр.081) + /api/practice/progress|attempt + LS.practiceProgressList/Submit
- фича-флаг trainer: тумблер в админке (Модули), requireFeature, FEATURE_HREFS (скрытие сайдбара+редирект), MODULE_CATALOG
- fix: подключён Lucide CDN на странице (иначе иконки сайдбара пустые)
- тесты practice.test.js (10/10); план развития plans/ai-trainer/PLAN.md

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

js/api.js

@@ -856,6 +856,7 @@ const FEATURE_HREFS = {
   exam9:         ['/exam9', '/exam9.html'],
   textbooks:     ['/textbooks', '/textbooks.html', '/textbook'],
   quantik:       ['/quantik', '/quantik.html'],
+  trainer:       ['/trainer', '/trainer.html'],
   theory:        ['/theory', '/theory.html'],
   sitemap:       ['/sitemap', '/sitemap.html'],
   wishes:        ['/wishes', '/wishes.html'],
@@ -1183,6 +1184,7 @@ window.LS = {
   customSimsList, customSimGet, customSimCreate, customSimUpdate, customSimDelete,
   customSimShare, customSimClone, customSimRelated, customSimAddLink, customSimDelLink,
   gameProgressList, gameProgressSubmit,
+  practiceProgressList, practiceSubmit,
   assistantContext, assistantSeen, assistantDismiss, assistantSettings, assistantAsk, assistantAskStream, assistantFlashcards, assistantQuestions, assistantFeedback, assistantMemory, assistantMemoryClear, imageGen, imageGenStatus,
   adminGetAssistant, adminSaveAssistant, adminTestAssistant, adminReindexTextbooks,
   adminSaveProvider, adminDeleteProvider, adminSetActiveProvider, adminAssistantModels,
@@ -1418,6 +1420,8 @@ async function customSimAddLink(id, d)  { return req('POST',   `/custom-sims/${i
 async function customSimDelLink(id, lid){ return req('DELETE', `/custom-sims/${id}/links/${lid}`); }
 async function gameProgressList()       { return req('GET',    '/game/progress'); }
 async function gameProgressSubmit(levelId, d) { return req('POST', '/game/progress', { level_id: levelId, time_ms: d && d.time_ms, stars: d && d.stars }); }
+async function practiceProgressList()   { return req('GET',    '/practice/progress'); }
+async function practiceSubmit(skill, correct) { return req('POST', '/practice/attempt', { skill, correct: !!correct }); }
 async function assistantContext()    { return req('GET',    '/assistant/context'); }
 async function assistantSeen(ruleId) { return req('POST',   '/assistant/seen', { ruleId }); }
 async function assistantDismiss(rid) { return req('POST',   '/assistant/dismiss', { ruleId: rid }); }