feat(place/booking-notifier): email booking reminders before booking start

[KesterJJ]

Superseded by #638, which carries this work plus the review fixes (reminder attachments, approver merge fields, owner-flag zone skip, network credentials removed from the trigger) and the added spec coverage (cron-driven sweep, two offsets on one booking, locker instance, advertised fields vs sent args).

[KesterJJ]

CI notes for this branch:

• Subset Report - crystal: latest, stable: true passes.
• Style / crystal-style fails on six files that are already unformatted on master (orbility/approvals.cr, leviton/acquisuite_spec.cr, ashrae/bacnet_vav_control.cr, place/booking_check_in_helper.cr, place/bookings/security_booking_check_in.cr, open_ai/voice_control.cr). crystal tool format was applied to the two files changed in this PR and neither of them is in that list.
• The nightly runs (Subset Report, Full Report) stop before running any tests with Error connecting to 'localhost:8080': Connection refused, i.e. the harness is unreachable in those jobs - the same environment problem as fix(place/bookings): PPT-2426 resolve asset names from Asset records #636.

Local validation: ./harness report drivers/place/booking_notifier.cr --no-colour --basic-render --verbose passes (1 tested, 0 failures, 0 timeouts); the baseline before the change passed too.