Add pagination to admin user activity endpoint #539

Bug Description

The getUserActivity method in src/modules/admin/admin-users.service.ts (lines 267-357) queries multiple tables without pagination, returning ALL activity records for a user. For long-tenured users, this could return thousands of records.

Location

src/modules/admin/admin-users.service.ts lines 267-357

async getUserActivity(userId: string): Promise<
    Array<{
        type: string;
        title: string;
        timestamp: Date;
        details: Record<string, unknown>;
    }>
> {
    // Fetch all activity sources - NO PAGINATION
    const [enrollmentRows, submissionRows, credentialRows] = await Promise.all([
        db.select()...from(enrollments)...where(eq(enrollments.userId, userId)),
        db.select()...from(quizSubmissions)...where(eq(quizSubmissions.userId, userId)),
        db.select()...from(credentials)...where(eq(credentials.userId, userId)),
    ]);
    // ... combines all and sorts
}

The Problem

1. No pagination - returns ALL records
2. For active users, this could be hundreds of enrollments, thousands of quiz submissions
3. The response is unbounded and could be very large
4. No limit on the number of records returned from each table
5. Combines all results in memory, sorts, and returns everything

Recommended Fix

Add pagination parameters and limit the query:

async getUserActivity(
    userId: string,
    page: number = 1,
    limit: number = 50
): Promise<{ activities: Activity[]; total: number }> {
    const offset = (page - 1) * limit;

    // Use UNION ALL query or limit each source
    // ... with pagination
}

Acceptance Criteria

• Add pagination parameters (page, limit) to the method
• Limit the number of records returned from each table
• Return total count for pagination metadata
• Consider using a UNION ALL query for efficiency

Severity

medium - Performance issue that could cause timeouts or memory issues for active users.