feat: implement user activity timeline and integrate supporting fixes

[Shadow-MMN]

Description

This PR introduces a secure, user-facing activity history feature built on top of the existing AuditLog system. It exposes user-scoped activity data through new API endpoints and enables CSV export of historical activity records.

Summary of Changes

New Features

• Added GET /users/me/activities for paginated user activity timeline
• Added GET /users/me/activities/export for CSV export of activity history
• Introduced UserActivityController to expose audit logs to authenticated users
• Created UsersModule to encapsulate user-related API logic

Security Improvements

• Strict enforcement of req.user.id for all activity queries
• Prevented cross-user access to audit logs
• Ensured export endpoint respects same access constraints as timeline

Integration

• Reused existing AuditLog infrastructure
• Leveraged AuditLogService for querying and filtering
• Leveraged AuditExportService for CSV generation

Testing

• Added E2E tests covering:

• • Pagination
• • Filtering by activity type
• • CSV export functionality
• • Access control validation

Fixes Included

During implementation, several existing issues in the codebase were resolved:

• Fixed dependency injection issues in index optimization services
• Fixed type mismatches in invoice and courses modules
• Corrected audit log field mapping in data retention service

Notes

• No new audit storage layer was introduced; existing infrastructure was fully reused
• No changes were made to frontend; this PR is backend-only and provides API support for future UI integration
• System remains fully backward compatible

Closes #553

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[RUKAYAT-CODER]

Kindly resolve conflict.

[Shadow-MMN]

Kindly resolve conflict.

On it

[Shadow-MMN]

@RUKAYAT-CODER , check it out now.

[RUKAYAT-CODER]

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