fix: preserve platform access for stardances who turn 19

[0xDracula]

fixes an issue where stardancers who joined before they turn 19 can't participate anymore when they turn 19

show it works?

I used rails console to mimic the situation

user = User.create!(
  email: "turns19demo@example.com",
  display_name: "demo_nineteen_#{rand(1000)}",
  age_attestation: "teen_13_18",
  experience_level: "some",
  interests: ["web_dev"],
  onboarded_at: 1.year.ago,
  verification_status: "verified",
  ysws_eligible: true
)

user.update_columns(created_at: 1.year.ago)
service = Sessions::HCALoginService.new(auth: nil, current_user: nil)
birthday = Date.current - 19.years
result = service.send(:hca_age_attestation, user, { ysws_eligible: false, birthday: birthday })
puts result # should be teen even tho they're 19 but created_at is 1 year ago

ai?
writing test file & rails console queries

closes #738