Fix event name search filter on admin activities page

[maebeale]

What is the goal of this PR and why is this important?

• The "Event Name" search field on /admin/activities/events was not filtering results at all
• The view sent params[:name] but the controller never applied it as a filter

How did you approach the change?

• Added a LIKE query filter in AhoyActivitiesController#index that does substring matching on ahoy_events.name
• Used sanitize_sql_like to prevent SQL injection from wildcard characters
• Added two request specs: exact name match and partial/substring match

UI Testing Checklist

• Visit /admin/activities/events, type an event name (e.g. "auth.login"), click Filter — only matching events appear
• Try a partial name (e.g. "bookmark") — only events containing that substring appear
• Clear the field and filter — all events appear again

Anything else to add?

N/A

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