* Add Slack admin modals + App Home admin section
Replace the two most error-prone positional admin commands with Block Kit
modals (override and holiday-add) opened from a new App Home admin section,
while keeping the typed subcommands as a fallback. Validation and side
effects are factored into shared helpers so the modal and command paths
can't drift, and every action/view handler re-checks is_admin against
get_admin_users() so a modal opened from Home can't bypass authorization.
Adds Schedule.list_overrides for the upcoming-overrides overview.
Refs: #136
* Update changelog date to July 02, 2026
* Add point-and-click admin actions in Slack for easier overrides and holidays
* [#136] Add admin UI evaluation spike doc (#140)
Co-authored-by: seahaven-openswe[bot] <296972425+seahaven-openswe[bot]@users.noreply.github.com>
Co-authored-by: amoussa1229 <166072409+amoussa1229@users.noreply.github.com>
