feat(l10n): add Arabic translations for new labels

- Add Arabic translations for 'headline', 'topic', and 'source'
- Include descriptions for new labels in both Arabic and English files
- Maintain consistency in translation style and formatting

Author: fulleni

lib/l10n/arb/app_ar.arb

@@ -107,14 +107,26 @@
   "@headlines": {
     "description": "تسمية الصفحة الفرعية للعناوين الرئيسية"
   },
+  "headline": "العنوان الرئيسي",
+  "@headline": {
+    "description": "تسمية العنوان الرئيسي"
+  },
   "topics": "المواضيع",
   "@topics": {
     "description": "تسمية الصفحة الفرعية للمواضيع"
   },
+  "topic": "الموضوع",
+  "@topic": {
+    "description": "تسمية الموضوع"
+  },
   "sources": "المصادر",
   "@sources": {
     "description": "تسمية الصفحة الفرعية للمصادر"
   },
+  "source": "المصدر",
+  "@source": {
+    "description": "تسمية المصدر"
+  },
   "appConfiguration": "إعدادات التطبيق",
   "@appConfiguration": {
     "description": "تسمية عنصر التنقل لإعدادات التطبيق"

lib/l10n/arb/app_en.arb

@@ -107,14 +107,26 @@
   "@headlines": {
     "description": "Label for the headlines subpage"
   },
+  "headline": "Headline",
+  "@headline": {
+    "description": "Label for the a singular headline"
+  },
   "topics": "Topics",
   "@topics": {
     "description": "Label for the topics subpage"
   },
+  "topic": "Topic",
+  "@topic": {
+    "description": "Label for the a singular topic"
+  },
   "sources": "Sources",
   "@sources": {
     "description": "Label for the sources subpage"
   },
+  "source": "Source",
+  "@source": {
+    "description": "Label for the a singular source"
+  },
   "appConfiguration": "App Configuration",
   "@appConfiguration": {
     "description": "Label for the app configuration navigation item"