Delete the non-functional suggestions widgetry in recurring event creation

[inducer]

Not much of an XSS because the source data is under instructor control.

[Copilot]

Pull request overview

Fixes unsafe HTML generation in the calendar’s ListTextWidget datalist/options rendering by switching to Django’s HTML formatting helpers, reducing the risk of XSS from unescaped values.

Changes:

• Use django.utils.html.format_html and format_html_join to build <datalist> and <option> elements with proper escaping.
• Add HTML formatting utilities import for safe rendering.

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[inducer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Implemented in 3a909d2. I applied both review items from that thread: removed mark_safe from ListTextWidget.render() in favor of format_html("{}{}", ...), and added a regression test (ListTextWidgetTest) that verifies unsafe option values/labels are escaped in the rendered datalist output. No UI-visible change, so no screenshot is applicable.