fix(analytics): show per-student last seen from login and session activity (#674)

* fix(analytics): show per-student last seen from login and session activity

Return ISO last-seen timestamps from course analytics instead of
pre-formatted strings so the dashboard can format them per student.
Batch-fetch last seen for all students and include session activity
alongside login events for more accurate, distinct values.

Co-authored-by: Rotimi Best <[email protected]>

* fix(analytics): destructure first row from getLastLogin query results

Promise.all returns an array per Drizzle select; nested destructuring
is required so loggedInAt and updatedAt are read from row objects.

Co-authored-by: Rotimi Best <[email protected]>

---------

Co-authored-by: Cursor Agent <[email protected]>
Co-authored-by: Rotimi Best <[email protected]>

apps/dashboard/src/lib/features/course/components/analytics/student-table.svelte

@@ -8,6 +8,7 @@
   import * as Table from '@cio/ui/base/table';
 
   import { courseApi } from '$features/course/api';
+  import { calDateDiff } from '$lib/utils/functions/date';
   import { t } from '$lib/utils/functions/translations';
 
   import EmptyState from './empty-state.svelte';
@@ -125,7 +126,7 @@
             </Table.Cell>
             <Table.Cell class="min-w-[120px] px-4 py-3">
               <span class="ui:text-muted-foreground text-sm">
-                {student.lastSeen}
+                {student.lastSeen ? calDateDiff(student.lastSeen) : $t('analytics.a_while_ago')}
               </span>
             </Table.Cell>
             <Table.Cell class="min-w-[120px] px-4 py-3">

apps/dashboard/src/lib/utils/types/analytics.ts

@@ -21,7 +21,7 @@ export interface StudentOverview {
   exercisesSubmitted: number;
   totalExercises: number;
   averageGrade: number;
-  lastSeen: string;
+  lastSeen: string | undefined;
   progressPercentage: number;
 }