StatusBar and InfoPanel sat above AppWindow in app.slint, which read as
though they were part of the application shell. They are not: neither is
instantiated anywhere but the develop view, and the shell's actual job --
choosing which of the five screens is up -- is easier to follow without
two unrelated components standing in front of it.
Moved verbatim to develop.slint, matching src/develop.rs. No behaviour
change; app.slint loses 232 lines and gains one import.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>