fix: correct last-sync date and logout redirect issues

- Fix admin users last-sync showing 1970 instead of actual sync date
  - Changed from MAX(qsos.createdAt) to MAX(syncJobs.completedAt)
  - Added timestamp conversion (seconds to milliseconds) for proper Date serialization
- Fix logout redirect not working from admin dashboard
  - Changed from goto() to window.location.href for hard redirect
  - Ensures proper navigation after auth state changes

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

src/backend/services/admin.service.js

@@ -127,7 +127,12 @@ export async function getUserStats() {
       lotwConfirmed: sql`CAST(SUM(CASE WHEN ${qsos.lotwQslRstatus} = 'Y' THEN 1 ELSE 0 END) AS INTEGER)`,
       dclConfirmed: sql`CAST(SUM(CASE WHEN ${qsos.dclQslRstatus} = 'Y' THEN 1 ELSE 0 END) AS INTEGER)`,
       totalConfirmed: sql`CAST(SUM(CASE WHEN ${qsos.lotwQslRstatus} = 'Y' OR ${qsos.dclQslRstatus} = 'Y' THEN 1 ELSE 0 END) AS INTEGER)`,
-      lastSync: sql`MAX(${qsos.createdAt})`,
+      lastSync: sql`(
+        SELECT MAX(${syncJobs.completedAt})
+        FROM ${syncJobs}
+        WHERE ${syncJobs.userId} = ${users.id}
+        AND ${syncJobs.status} = 'completed'
+      )`.mapWith(Number),
       createdAt: users.createdAt,
     })
     .from(users)
@@ -135,7 +140,11 @@ export async function getUserStats() {
     .groupBy(users.id)
     .orderBy(sql`COUNT(${qsos.id}) DESC`);
 
-  return stats;
+  // Convert lastSync timestamps (seconds) to Date objects for JSON serialization
+  return stats.map(stat => ({
+    ...stat,
+    lastSync: stat.lastSync ? new Date(stat.lastSync * 1000) : null,
+  }));
 }
 
 /**