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/components/Header.jsx

@@ -10,13 +10,18 @@ import ThemeToggle from './ThemeToggle'
 const PAGE_TITLE_KEYS = {
   '/': 'header.dashboard',
   '/posts': 'header.posts',
+  '/calendar': 'header.calendar',
   '/assets': 'header.assets',
+  '/artefacts': 'header.artefacts',
   '/campaigns': 'header.campaigns',
+  '/brands': 'header.brands',
   '/finance': 'header.finance',
+  '/budgets': 'header.budgets',
   '/projects': 'header.projects',
   '/tasks': 'header.tasks',
+  '/issues': 'header.issues',
   '/team': 'header.team',
-  '/users': 'header.users',
+  '/settings': 'header.settings',
 }
 
 const ROLE_INFO = {