feat: Reminder Manager UX — timeline-first grouped layout

Replace 3-row filter panel with a grouped feed (Überfällig / Diese Woche /
Dieser Monat / Später). KPI cards are now clickable shortcuts that filter to
their time horizon or type (Pre-Market). Filter bar condenses to one row:
search + type dropdown + archive toggle. Rows get a left priority-color
border (red/orange/yellow). Default status filter is ACTIVE+SNOOZED.

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

src/services/reminderService.ts

@@ -48,6 +48,8 @@ export const reminderService = {
         (r.shadowMarketRisk === ShadowMarketRisk.HIGH),
     ).length
 
+    const overdueCount = active.filter(r => daysDiff(r.dueDate) <= 0).length
+
     const activeDays = active
       .filter(r => daysDiff(r.dueDate) > 0)
       .map(r => daysDiff(r.dueDate))
@@ -60,6 +62,7 @@ export const reminderService = {
       dueThisWeek,
       dueThisMonth,
       schattenmarktReadyCount,
+      overdueCount,
       avgDaysToAction,
     }
   },