feat(materials): Фаза 5 — заметка в флешкарты

Кнопка «В флешкарты» на карточке-заметке: выбор колоды (или новая «Из материалов») →
создание карточки (front=заголовок, back=текст) через существующий API флешкард.
Хелперы fcListDecks/fcCreateDeck/fcAddCard в js/api.js.

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

js/api.js

@@ -1050,6 +1050,7 @@ window.LS = {
   crAdminGetAllHistory, crAdminGetTeachersList,
   listMaterials, saveMaterial, updateMaterial, deleteMaterial,
   createMaterialCollection, updateMaterialCollection, deleteMaterialCollection,
+  fcListDecks, fcCreateDeck, fcAddCard,
   escapeHtml, esc,
   parseDate, fmtRelTime, safeHref,
   initPage,
@@ -1251,6 +1252,9 @@ async function deleteMaterial(id)     { return req('DELETE', `/materials/${id}`)
 async function createMaterialCollection(d)   { return req('POST',   '/materials/collections', d); }
 async function updateMaterialCollection(id,d){ return req('PATCH',  `/materials/collections/${id}`, d); }
 async function deleteMaterialCollection(id)  { return req('DELETE', `/materials/collections/${id}`); }
+async function fcListDecks()         { return req('GET',  '/flashcards/decks'); }
+async function fcCreateDeck(d)       { return req('POST', '/flashcards/decks', d); }
+async function fcAddCard(deckId, d)  { return req('POST', `/flashcards/decks/${deckId}/cards`, d); }
 async function deleteFile(id)                        { return req('DELETE', `/files/${id}`); }
 async function getFileAccess(id)                     { return req('GET',    `/files/${id}/access`); }
 async function assignFile(id, data)                  { return req('POST',   `/files/${id}/assign`, data); }