Fix accordion being dead after LiveView live navigation. Its toggle logic lived
in a per-instance inline <script>, which LiveView does not execute when content
is injected via a navigate link - so clicks did nothing, and stale listeners
from earlier full loads could throw a null classList error. Move the behaviour
into the shipped JS bundle, registered once and surviving navigation. Requires
importing the bundle (already needed for the input/Chat components). Update the
upgrade guide and add a regression test asserting no inline <script>.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>