Right-rail preview was rendered server-side via {{if eq $f.Kind ...}},
so it stayed on whatever kind the page loaded with. Editing an SMTP
channel and flipping to ntfy in the picker left the email RFC 5322
sample on screen.
Render all three preview panels with id='preview-<kind>' (only the
matching one visible on first render) and toggle their .hidden class
in the kind-switcher JS alongside the field panels. Same pattern
used for fields-<kind>.
steve
bd310d918b