feat(i18n, frontend): enhance course planning with optional steps and localization updates

- Added a new section for optional learning steps in the course planning UI, allowing users to engage with additional content when no mandatory tasks are due.
- Updated localization files for Cebuano, German, English, Spanish, and French to reflect changes in course planning instructions and titles, ensuring clarity and consistency across languages.
- Improved pedagogical logic for lesson recommendations, focusing on cognitive load and spaced repetition principles to enhance user learning experience.

frontend/src/views/social/VocabCourseView.vue

@@ -74,6 +74,26 @@
             </li>
           </ol>
         </div>
+        <div v-else-if="showTodayPlanSoftOptional" class="course-today-plan course-today-plan--soft">
+          <h4 class="course-today-plan__title">{{ $t('socialnetwork.vocab.courses.courseTodayPlanSoftTitle') }}</h4>
+          <p class="course-today-plan__intro">{{ $t('socialnetwork.vocab.courses.courseTodayPlanSoftIntro') }}</p>
+          <ol class="course-today-plan__list">
+            <li
+              v-for="(step, idx) in todayPlanOptionalSteps"
+              :key="`opt-${step.type}-${step.lesson.id}-${idx}`"
+              class="course-today-plan__item"
+            >
+              <div class="course-today-plan__item-main">
+                <span class="course-today-plan__step-label">{{ todayPlanStepLabel(step.type) }}</span>
+                <span class="course-today-plan__lesson-title">{{ step.lesson.title }}</span>
+                <span class="course-today-plan__lesson-meta">#{{ step.lesson.lessonNumber }}</span>
+              </div>
+              <button type="button" class="course-today-plan__action course-today-plan__action--soft" @click="openTodayPlanStep(step)">
+                {{ step.type === 'practice' ? $t('socialnetwork.vocab.courses.courseTodayPlanTrainer') : $t('socialnetwork.vocab.courses.courseTodayPlanOpen') }}
+              </button>
+            </li>
+          </ol>
+        </div>
         <div v-else class="course-today-plan course-today-plan--empty">
           <h4 class="course-today-plan__title">{{ $t('socialnetwork.vocab.courses.courseTodayPlanTitle') }}</h4>
           <p class="course-today-plan__intro">{{ $t('socialnetwork.vocab.courses.courseTodayPlanEmpty') }}</p>
@@ -400,6 +420,15 @@ export default {
         })
         .slice(0, 4);
     },
+    /**
+     * Didaktischer Tagesvorschlag (nicht Kalender-fixiert, aber nach Prinzipien):
+     * 1) Spacing: fällige Kurz-Wiederholungen zuerst (Abruf vor neuem Input).
+     * 2) Kognitive Last: nur eine begrenzte „Einheit“ neuer Block-Lektionen pro Aufruf,
+     *    schwere/checkpoint/intensive Lektionen zählen stärker (siehe pickPedagogicalBlockSteps).
+     * 3) Dann Intensivphase, wenn freigeschaltet.
+     * Keine „Fallbacks“ in dieser Liste: weitere Lektion/Trainer nur unter
+     * todayPlanOptionalSteps mit eigener Einleitung (Pause/Spacing sinnvoller als Pflicht).
+     */
     todayRecommendedSteps() {
       const out = [];
       const seen = new Set();
@@ -411,20 +440,36 @@ export default {
         out.push({ type, lesson });
       };
       this.dueReviewLessons.forEach((l) => push('review_due', l));
-      this.currentBlockLessons.slice(0, 3).forEach((l) => push('block', l));
+      this.pickPedagogicalBlockSteps().forEach((l) => push('block', l));
       if (this.nextIntensiveReviewLesson) {
         push('intensive', this.nextIntensiveReviewLesson);
       }
-      if (out.length === 0 && this.currentLesson) {
+      return out.slice(0, 8);
+    },
+    /** Optional: nur wenn kein didaktischer Pflichtplan – semantisch „könntest du, Pause oft besser“. */
+    todayPlanOptionalSteps() {
+      const out = [];
+      const seen = new Set();
+      const push = (type, lesson) => {
+        if (!lesson?.id || seen.has(lesson.id)) {
+          return;
+        }
+        seen.add(lesson.id);
+        out.push({ type, lesson });
+      };
+      if (this.currentLesson) {
         const p = this.getLessonProgress(this.currentLesson.id, this.currentLesson);
         if (!p?.completed) {
           push('continue', this.currentLesson);
         }
       }
-      if (out.length === 0 && this.freePracticeLessons.length > 0) {
+      if (this.freePracticeLessons.length > 0) {
         push('practice', this.freePracticeLessons[0]);
       }
-      return out.slice(0, 8);
+      return out;
+    },
+    showTodayPlanSoftOptional() {
+      return this.todayRecommendedSteps.length === 0 && this.todayPlanOptionalSteps.length > 0;
     },
     isLessonNumberValid() {
       return Number(this.newLesson.lessonNumber) > 0;
@@ -510,6 +555,45 @@ export default {
       const progress = this.getLessonProgress(lessonId, lesson);
       return progress?.lastAccessedAt || progress?.completedAt || progress?.updatedAt || '';
     },
+    /**
+     * Grobe „Last-Einheit“ pro Lektion für Tageskappung (1 = leicht, 2 = schwer/Checkpoint/Intensiv im Block).
+     */
+    blockLessonDailyLoadUnits(lesson) {
+      if (!lesson) {
+        return 1;
+      }
+      const p = lesson.pedagogy || {};
+      const mode = p.didacticMode;
+      if (mode === 'checkpoint' || mode === 'intensive_review' || p.isIntensiveReview) {
+        return 2;
+      }
+      const w = Number(p.difficultyWeight);
+      if (Number.isFinite(w) && w >= 4) {
+        return 2;
+      }
+      return 1;
+    },
+    /**
+     * Offene Lektionen im Block nach Nummer, mit Obergrenze für „neues Material“ pro Empfehlungsliste
+     * (Spacing + cognitive load: nicht drei schwere Lektionen auf einmal).
+     */
+    pickPedagogicalBlockSteps() {
+      const list = [...this.currentBlockLessons].sort(
+        (a, b) => Number(a.lessonNumber) - Number(b.lessonNumber)
+      );
+      const MAX_UNITS = 3;
+      const picked = [];
+      let units = 0;
+      for (const l of list) {
+        const cost = this.blockLessonDailyLoadUnits(l);
+        if (units + cost > MAX_UNITS) {
+          break;
+        }
+        picked.push(l);
+        units += cost;
+      }
+      return picked;
+    },
     daysSince(dateString) {
       if (!dateString) {
         return 0;
@@ -1360,6 +1444,11 @@ export default {
   border: 1px solid rgba(212, 184, 150, 0.45);
 }
 
+.course-today-plan--soft {
+  border-style: dashed;
+  opacity: 0.95;
+}
+
 .course-today-plan--empty {
   background: rgba(250, 250, 250, 0.85);
   border-color: var(--color-border, #e0dcd6);
@@ -1433,6 +1522,10 @@ export default {
   cursor: pointer;
 }
 
+.course-today-plan__action--soft {
+  font-weight: normal;
+}
+
 .course-today-plan__action:hover {
   border-color: #b8a896;
   background: #fff;