Add venue, start, and end times to events model

[experimatt]

Add venue, start_time, and end_time fields to Event model and use them in the meta description.

e.g. "Minnebar 19 is a participant-led unconference free and open to all. It’ll be held on Saturday, May 3rd, 2025, 8:00 am – 6:30 pm CDT"

# draft that doesn't include dynamic values for start & end time, or include the venue yet.

"#{Event.current_event.name} is a participant-led unconference free and open to all. It'll be held on #{Event.current_event.date.strftime('%A, %B %e, %Y')}, 8:00 am – 6:30 pm CDT"

[experimatt]

This might not actually be needed. We can probably just stick with hard-coded values, as Best Buy HQ and the start/end times haven't diverged except for the year Minnebar went virtual.

[pcantrell]

I’d consider computing them from the associated timeslots.

[experimatt]

@pcantrell good idea, although we'd still need to show a default value before timeslots have been created - because this will be shown in meta tags well before we're ready to actually set the schedule.