M3's scaffold is bars, then rails, then panes, and the shell had no slot that
rendered above the rail: an application-wide bar could only be a pane bar beside
it. `banner` is that slot — the shell is a column now, with the rail and the page
as one row inside it — and the rail sticks under a pinned banner through
--material-banner rather than behind it. `top` still means the page's own bar.
Plan: docs/plans/material-3-alignment.md, step 21 (navigation N-14).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
