Write up the 2.0.2 hardening for upgraders

Collect the changed defaults in the release notes with what to set to restore
the previous behaviour, and record content-based dispatch in the threat model.
The existing service-dispatcher row claimed dispatchers only validate service
existence, which understated what late binding allowed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>