Add default reminder email template

[mapiolca]

Summary

• create an idempotent default weekly reminder email template during module initialization and set it as the default when not configured
• add helper functions to resolve, create, and select the template using Dolibarr email template classes
• provide English and French translations for the default reminder template label, subject, and body

Testing

• php -l core/modules/modTimesheetWeek.class.php
• php -l class/timesheetweek_reminder.class.php

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Codex Task