feat: Phase B — interactive dashboard, breadcrumbs, clickable navigation
- Breadcrumb component: reusable nav with items array (label+href)
- DeadlineTrafficLights: buttons → Links to /fristen?status={filter}
- CaseOverviewGrid: static metrics → clickable Links to /cases?status={filter}
- UpcomingTimeline: items → clickable Links to /fristen/{id} or /termine/{id}
with case number links and hover chevron
- QuickActions: swap CalDAV Sync for "Neuer Termin" → /termine/neu,
fix "Frist eintragen" → /fristen/neu
- AISummaryCard: add RefreshCw button with spinning animation
- RecentActivityList: new component showing recent case events
- DeadlineList: accept initialStatus prop, add this_week/ok filters
- fristen/page.tsx: read searchParams.status for initial filter
- Add breadcrumbs to dashboard, fristen, cases, termine pages
- Add RecentActivity type, update DashboardData type
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