Add in-app reminders for lightning talk and open space sign-ups

[JacobCoffee]

Add push notification or in-app reminders for lightning talk sign-up windows and open space room reservations.

Lightning Talk Sign-Up Windows (all times PDT):

Fri May 16:

• Morning slot (8-9 AM): signup opens 9:00 AM, deadline 1:00 PM
• Evening slot (6-7 PM): signup opens 5:00 AM, deadline 9:00 AM

Sat May 17:

• Morning slot (8-9 AM): signup opens 9:00 AM, deadline 1:00 PM
• Afternoon slot (5:45-6:45 PM): signup opens 5:00 AM, deadline 9:00 AM

Open Space Room Reservations:

• Thu May 15 slots open at 5:00 AM PDT
• Fri May 16 slots open at 5:00 AM PDT
• Sat May 17 slots open at 5:00 AM PDT

Reminders should fire ~15 min before each signup window opens.

[linear]

PYMOBIL-106