Add per-user notification time preferences

Allow users to customize when they receive notification reminders:
- Add task_due_soon_hour, task_overdue_hour, warranty_expiring_hour fields
- Store times in UTC, clients convert to/from local timezone
- Worker runs hourly, queries only users scheduled for that hour
- Early exit optimization when no users need notifications
- Admin UI displays custom notification times

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

admin/src/app/(dashboard)/notification-prefs/page.tsx

@@ -4,9 +4,17 @@ import { useState } from 'react';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { ColumnDef } from '@tanstack/react-table';
 import Link from 'next/link';
-import { MoreHorizontal, Trash2 } from 'lucide-react';
+import { MoreHorizontal, Trash2, Clock } from 'lucide-react';
 
 import { notificationPrefsApi, type NotificationPreference } from '@/lib/api';
+
+// Helper function to format UTC hour for display
+function formatHour(hour: number | null): string {
+  if (hour === null) return '-';
+  const h = hour % 12 || 12;
+  const ampm = hour < 12 ? 'AM' : 'PM';
+  return `${h}:00 ${ampm}`;
+}
 import { DataTable } from '@/components/data-table';
 import { Button } from '@/components/ui/button';
 import { Switch } from '@/components/ui/switch';
@@ -166,6 +174,43 @@ export default function NotificationPrefsPage() {
         />
       ),
     },
+    {
+      id: 'notification_times',
+      header: () => (
+        <div className="flex items-center gap-1">
+          <Clock className="h-4 w-4" />
+          <span>Custom Times (UTC)</span>
+        </div>
+      ),
+      cell: ({ row }) => {
+        const { task_due_soon_hour, task_overdue_hour, warranty_expiring_hour } = row.original;
+        const hasCustomTimes = task_due_soon_hour !== null || task_overdue_hour !== null || warranty_expiring_hour !== null;
+
+        if (!hasCustomTimes) {
+          return <span className="text-muted-foreground text-sm">Default</span>;
+        }
+
+        return (
+          <div className="text-sm space-y-0.5">
+            {task_due_soon_hour !== null && (
+              <div className="text-xs">
+                <span className="text-muted-foreground">Due Soon:</span> {formatHour(task_due_soon_hour)}
+              </div>
+            )}
+            {task_overdue_hour !== null && (
+              <div className="text-xs">
+                <span className="text-muted-foreground">Overdue:</span> {formatHour(task_overdue_hour)}
+              </div>
+            )}
+            {warranty_expiring_hour !== null && (
+              <div className="text-xs">
+                <span className="text-muted-foreground">Warranty:</span> {formatHour(warranty_expiring_hour)}
+              </div>
+            )}
+          </div>
+        );
+      },
+    },
     {
       id: 'actions',
       cell: ({ row }) => {

admin/src/lib/api.ts

@@ -599,6 +599,10 @@ export interface NotificationPreference {
   warranty_expiring: boolean;
   // Email preferences
   email_task_completed: boolean;
+  // Custom notification times (UTC hour 0-23, null means use system default)
+  task_due_soon_hour: number | null;
+  task_overdue_hour: number | null;
+  warranty_expiring_hour: number | null;
   created_at: string;
   updated_at: string;
 }