Add docs/developer/lamni_smear_architecture.md covering the three-tier
device/ipython-client/GUI architecture this feature exercises: the
camera's two PreviewSignal channels (image vs smear_preview) and why
composite pushes needed their own channel, XRayEye.set_live_view_signal
and exactly when the caller must switch it back, the sweep algorithm
(non-blocking mv() + ScanReport.status polling + max-projection), and
the bw-generate-cli regeneration step required whenever a plugin
widget's USER_ACCESS changes (the cause of this session's confusing
AttributeError even after a full client/GUI restart).
Also expand the user-facing description in lamni.md with a note on the
live-updating composite display and a cross-reference to the new
developer page.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
