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/i18n/locales/en/socialnetwork.json

@@ -696,8 +696,8 @@
                 "quickReviewPromptTarget": "Type in target language: \"{term}\"",
                 "quickReviewAcknowledge": "Read, continue",
                 "courseTodayPlanTitle": "Suggested for today",
-                "courseTodayPlanIntro": "Practical order: first everything that is due for a quick review, then open lessons in your current block, then intensive review if shown. Quick reviews are three short revisit dates after you finish a lesson (typically about 1, 3 and 7 days apart) so vocabulary sticks.",
-                "courseTodayPlanIntroNoDueReview": "No quick review is due today. Start with the open lessons in your current block, then do intensive review if shown. Quick reviews reappear automatically on the 1/3/7-day rhythm.",
+                "courseTodayPlanIntro": "Pedagogical order: first every due quick review (spaced retrieval before new input). Then only a limited set of open lessons from your current block—harder, checkpoint or intensive lessons count double so the daily load stays manageable. Then intensive review if unlocked. Quick reviews are the three short revisit dates after a lesson (typically about 1, 3 and 7 days apart).",
+                "courseTodayPlanIntroNoDueReview": "No quick review is due today. You’ll see the next sensible steps in your current block only (capped by difficulty), then intensive review if shown. Quick reviews reappear automatically on the 1/3/7-day rhythm.",
                 "courseTodayPlanStepReviewDue": "Quick review now",
                 "courseTodayPlanStepBlock": "Continue in your current block",
                 "courseTodayPlanStepIntensive": "Intensive review",
@@ -706,6 +706,8 @@
                 "courseTodayPlanOpen": "Open lesson",
                 "courseTodayPlanTrainer": "Open trainer",
                 "courseTodayPlanEmpty": "Nothing scheduled as due right now and no clear next block step. Pick a lesson below or use free practice with the trainer.",
+                "courseTodayPlanSoftTitle": "Nothing required today — a break is fine",
+                "courseTodayPlanSoftIntro": "Spacing helps memory: nothing urgent is on your route right now. The items below are optional—often it is better pedagogy to continue tomorrow with a fresh mind.",
                 "courseFlowReviewStat": "Due review: {count}",
                 "courseFlowBlockStat": "Active block: {block}",
                 "courseFlowReviewTitle": "Due review",