fix: consistent page titles for all routes in header

Added missing title keys for calendar, artefacts, brands, budgets,
issues, and settings. No more fallback "Page" text.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src/i18n/ar.json

@@ -705,6 +705,12 @@
   "header.projects": "المشاريع",
   "header.tasks": "مهامي",
   "header.team": "الفريق",
+  "header.calendar": "تقويم المنشورات",
+  "header.artefacts": "المخرجات",
+  "header.brands": "العلامات التجارية",
+  "header.budgets": "الميزانيات",
+  "header.issues": "البلاغات",
+  "header.settings": "الإعدادات",
   "header.users": "إدارة المستخدمين",
   "header.projectDetails": "تفاصيل المشروع",
   "header.campaignDetails": "تفاصيل الحملة",