Three docs for three audiences: service-overview.md for anyone integrating
with or operating the service, implementation.md for engineers maintaining
this codebase, and frontend-notification-click-actions.md as a self-contained
handoff for the client team to start building tap-to-navigate against — it
flags the click_url URL format as an unconfirmed placeholder needing their
input, and catalogs every notification type currently sending one.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
