The HTML export feed, sidebar tree, and TUI session tree did not handle
the developer role, so plan content injected after /plan approval (and
any other developer messages) was hidden from /export and shown as a
bare [developer] label in /tree.
Renders developer messages in the main feed with a dimmed
.developer-message style, labels them in the sidebar tree, counts them
in header stats, and shows their content in the TUI tree selector so
search matches the body.
Closes#753.
Co-Authored-By: omp <noreply@oh-my-pi.dev>
David Marshall