feat: F001 app shell & global layout system

Add PageHeader, UserMenu, NotificationButton, OrganizationContextBadge,
RightContextPanel, CompareTray, and ActivityTimeline; wire all into AppShell.

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

src/pages/ops/ActivityTimeline.tsx

@@ -0,0 +1,16 @@
+import { Box, Typography } from '@mui/material'
+import { PageHeader } from '../../components/layout'
+
+export default function ActivityTimeline() {
+  return (
+    <Box sx={{ p: 3 }}>
+      <PageHeader
+        title="Aktivitäts-Timeline"
+        subtitle="Verlauf aller System- und Benutzeraktionen"
+      />
+      <Typography color="text.secondary" sx={{ mt: 3 }}>
+        Timeline wird implementiert...
+      </Typography>
+    </Box>
+  )
+}