feat(vocab): add grammar explanations to VocabLessonView and enhance localization

- Introduced new sections for grammar explanations in VocabLessonView, providing users with contextual insights during vocabulary lessons.
- Added localization keys in German, English, and Spanish for the new grammar explanation titles and introductions, improving user guidance across languages.
- Updated styles for the grammar explanation section to enhance visual clarity and user experience.

frontend/src/i18n/locales/de/socialnetwork.json

@@ -461,6 +461,8 @@
                 "learningGoals": "Lernziele",
                 "corePatterns": "Kernmuster",
                 "corePatternsHint": "Zuerst die Zielsprache lesen, darunter die deutsche Bedeutung — so lernst du jedes Muster bewusst in beiden Richtungen.",
+                "learningGrammarTitle": "Kurz die Grammatik einordnen",
+                "learningGrammarIntro": "Lies diese 1-2 Hinweise nach den Begriffen kurz durch. Danach gehst du mit mehr Orientierung in den Trainer.",
                 "vocabPrepTitle": "Vorbereitung vor dem Vokabeltrainer",
                 "vocabPrepStep1": "Lies Kernmuster und Wortliste (Deutsch ↔ Zielsprache) einmal in Ruhe durch.",
                 "vocabPrepProgress": "Durchgang {pass}: Begriff {current} von {total}",

frontend/src/i18n/locales/en/socialnetwork.json

@@ -461,6 +461,8 @@
                 "learningGoals": "Learning Goals",
                 "corePatterns": "Core Patterns",
                 "corePatternsHint": "Read the target language first, then the meaning below — you learn each pattern both ways.",
+                "learningGrammarTitle": "Briefly frame the grammar",
+                "learningGrammarIntro": "Read these 1-2 hints after the key terms. Then you go into the trainer with better orientation.",
                 "vocabPrepTitle": "Preparation before the vocabulary trainer",
                 "vocabPrepStep1": "Read through core patterns and the word list (native language ↔ target language) once.",
                 "vocabPrepProgress": "Pass {pass}: item {current} of {total}",

frontend/src/i18n/locales/es/socialnetwork.json

@@ -459,6 +459,8 @@
                 "learningGoals": "Objetivos",
                 "corePatterns": "Patrones básicos",
                 "corePatternsHint": "Primero la lengua meta; debajo, el significado en tu idioma.",
+                "learningGrammarTitle": "Ubicar brevemente la gramática",
+                "learningGrammarIntro": "Lee estas 1-2 pistas después de los términos clave. Así entras al entrenador con mejor orientación.",
                 "vocabPrepTitle": "Preparación antes del entrenador de vocabulario",
                 "vocabPrepStep1": "Lee una vez los patrones clave y la lista de palabras (idioma nativo ↔ lengua meta).",
                 "vocabPrepProgress": "Pasada {pass}: término {current} de {total}",