feat(bisaya-course): add new lesson and update course creation logic

- Introduced a new lesson titled "Zahlen & Preise" to enhance the numerical curriculum in Bisaya.
- Updated the course creation logic to check for existing "Familien"-Bisaya courses, ensuring idempotency in course creation.
- Enhanced the lesson didactics by mapping legacy titles to current lesson keys, improving data consistency.
- Adjusted the course generation script to limit Bisaya courses to German-speaking learners only, streamlining course offerings.

backend/scripts/migrate-bisaya-zahlen-split.js

@@ -0,0 +1,202 @@
+#!/usr/bin/env node
+/**
+ * Migriert ältere Bisaya-Kurse von einer kombinierten Lektion „Zahlen & Preise“ (nur #18)
+ * zur viergeteilten Zahlenreihe (#18–#21). Erwartet vorher noch das alte Layout:
+ * Lektion 19 = „Woche 2 - Wiederholung“ (liegt im neuen Kurs an Position 22).
+ *
+ * Ablauf je Kurs:
+ * - Lektionen mit lesson_number >= 19 um +3 nach oben schieben (von oben nach unten)
+ * - Lektion 18 auf „Zahlen 1–20“ setzen
+ * - Neue Lektionen 19–21 („Zahlen: Zehner/Hunderter/Tausender“) einfügen
+ *
+ * Verwendung:
+ *   node backend/scripts/migrate-bisaya-zahlen-split.js
+ *
+ * Anschließend:
+ *   node backend/scripts/update-bisaya-didactics.js
+ *   node backend/scripts/create-bisaya-course-content.js
+ */
+
+import { sequelize } from '../utils/sequelize.js';
+import VocabCourseLesson from '../models/community/vocab_course_lesson.js';
+import { LESSON_DIDACTICS } from './update-bisaya-didactics.js';
+import { getBisayaLessonPedagogy } from './bisaya-course-phase2-pedagogy.js';
+
+const INSERTED_LESSONS = [
+  {
+    lessonNumber: 19,
+    title: 'Zahlen: Zehner',
+    description: 'Runde Zehner von 20 bis 90',
+    weekNumber: 2,
+    dayNumber: 4,
+    lessonType: 'vocab',
+    culturalNotes: null,
+    targetMinutes: 20,
+    targetScorePercent: 85,
+    requiresReview: true
+  },
+  {
+    lessonNumber: 20,
+    title: 'Zahlen: Hunderter',
+    description: 'Hunderter bis 900 (usa ka gatos … siyam ka gatos)',
+    weekNumber: 2,
+    dayNumber: 4,
+    lessonType: 'vocab',
+    culturalNotes: null,
+    targetMinutes: 20,
+    targetScorePercent: 85,
+    requiresReview: true
+  },
+  {
+    lessonNumber: 21,
+    title: 'Zahlen: Tausender',
+    description: 'Tausender und große Beträge (libo)',
+    weekNumber: 2,
+    dayNumber: 4,
+    lessonType: 'vocab',
+    culturalNotes: null,
+    targetMinutes: 18,
+    targetScorePercent: 85,
+    requiresReview: true
+  }
+];
+
+function applyPedagogy(patch, lessonNumber) {
+  const pedagogy = getBisayaLessonPedagogy(lessonNumber) || {};
+  patch.didacticMode = pedagogy.didacticMode || null;
+  patch.phaseLabel = pedagogy.phaseLabel || null;
+  patch.blockNumber = pedagogy.blockNumber ?? null;
+  patch.difficultyWeight = pedagogy.difficultyWeight ?? null;
+  patch.newUnitTarget = pedagogy.newUnitTarget ?? null;
+  patch.reviewWeight = pedagogy.reviewWeight ?? null;
+  patch.isIntensiveReview = Boolean(pedagogy.isIntensiveReview);
+}
+
+function applyDidactics(patch, title) {
+  const d = LESSON_DIDACTICS[title];
+  if (!d) return;
+  patch.learningGoals = d.learningGoals || [];
+  patch.corePatterns = d.corePatterns || [];
+  patch.grammarFocus = d.grammarFocus || [];
+  patch.speakingPrompts = d.speakingPrompts || [];
+  patch.practicalTasks = d.practicalTasks || [];
+}
+
+async function migrateCourse(courseId) {
+  const maxRow = await sequelize.query(
+    `SELECT MAX(lesson_number) AS max FROM community.vocab_course_lesson WHERE course_id = :courseId`,
+    { replacements: { courseId }, type: sequelize.QueryTypes.SELECT }
+  );
+  const maxNum = Number(maxRow[0]?.max || 0);
+  if (maxNum < 19) {
+    return { status: 'skip', reason: 'weniger als 19 Lektionen' };
+  }
+
+  const l19 = await VocabCourseLesson.findOne({
+    where: { courseId, lessonNumber: 19 }
+  });
+  if (!l19) {
+    return { status: 'skip', reason: 'keine Lektion 19' };
+  }
+  if (l19.title !== 'Woche 2 - Wiederholung') {
+    return { status: 'skip', reason: 'Lektion 19 ist nicht „Woche 2 - Wiederholung“ (bereits migriert oder anderer Stand)' };
+  }
+
+  const l18 = await VocabCourseLesson.findOne({
+    where: { courseId, lessonNumber: 18 }
+  });
+  if (!l18) {
+    return { status: 'skip', reason: 'keine Lektion 18' };
+  }
+  if (l18.title !== 'Zahlen & Preise' && l18.title !== 'Zahlen 1–20') {
+    return { status: 'skip', reason: `Lektion 18 unerwartet: „${l18.title}“` };
+  }
+
+  await sequelize.transaction(async (t) => {
+    for (let n = maxNum; n >= 19; n -= 1) {
+      await VocabCourseLesson.update(
+        { lessonNumber: n + 3 },
+        { where: { courseId, lessonNumber: n }, transaction: t }
+      );
+    }
+
+    const lesson18 = await VocabCourseLesson.findOne({
+      where: { courseId, lessonNumber: 18 },
+      transaction: t
+    });
+    const patch18 = {
+      title: 'Zahlen 1–20',
+      description: 'Grundzahlen und Zahlen bis 20 (usa … baynte)',
+      weekNumber: 2,
+      dayNumber: 4,
+      lessonType: 'vocab',
+      culturalNotes: null,
+      targetMinutes: 22,
+      targetScorePercent: 85,
+      requiresReview: true
+    };
+    applyDidactics(patch18, 'Zahlen 1–20');
+    applyPedagogy(patch18, 18);
+    await lesson18.update(patch18, { transaction: t });
+
+    for (const def of INSERTED_LESSONS) {
+      const createPayload = {
+        courseId,
+        chapterId: null,
+        lessonNumber: def.lessonNumber,
+        title: def.title,
+        description: def.description,
+        weekNumber: def.weekNumber,
+        dayNumber: def.dayNumber,
+        lessonType: def.lessonType,
+        culturalNotes: def.culturalNotes,
+        targetMinutes: def.targetMinutes,
+        targetScorePercent: def.targetScorePercent,
+        requiresReview: def.requiresReview
+      };
+      applyDidactics(createPayload, def.title);
+      applyPedagogy(createPayload, def.lessonNumber);
+      await VocabCourseLesson.create(createPayload, { transaction: t });
+    }
+  });
+
+  return { status: 'ok' };
+}
+
+async function main() {
+  await sequelize.authenticate();
+
+  const [bisayaLanguage] = await sequelize.query(
+    `SELECT id FROM community.vocab_language WHERE name = 'Bisaya' LIMIT 1`,
+    { type: sequelize.QueryTypes.SELECT }
+  );
+  if (!bisayaLanguage) {
+    console.error('❌ Bisaya-Sprache nicht gefunden.');
+    process.exit(1);
+  }
+
+  const courses = await sequelize.query(
+    `SELECT id, title FROM community.vocab_course WHERE language_id = :languageId ORDER BY id`,
+    { replacements: { languageId: bisayaLanguage.id }, type: sequelize.QueryTypes.SELECT }
+  );
+
+  console.log(`Gefunden: ${courses.length} Bisaya-Kurs(e)\n`);
+
+  for (const course of courses) {
+    const result = await migrateCourse(course.id);
+    if (result.status === 'ok') {
+      console.log(`✅ Kurs ${course.id}: „${course.title}“ – Zahlen-Split angewendet (Lektionen verschoben, 19–21 eingefügt).`);
+    } else {
+      console.log(`⏭️  Kurs ${course.id}: „${course.title}“ – ${result.reason}`);
+    }
+  }
+
+  console.log('\nFertig. Danach: node backend/scripts/update-bisaya-didactics.js && node backend/scripts/create-bisaya-course-content.js');
+  await sequelize.close();
+}
+
+main().catch((e) => {
+  console.error('❌ Fehler:', e);
+  sequelize.close();
+  process.exit(1);
+});