Float the dashboard rail along the bottom on a phone

Below md a dashboard stacks to one column and dropped its rail. The rail is
now a horizontal row in the dashboard's own look, floated over the bottom
of the screen on /panel/{id} and above the dock in the app's view, with
44px items, sideways scrolling when it overflows, and padding so the last
tile clears it; a panel's read-only notice moves up out of its way. The
three looks share the geometry from ui/core.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013GAeg4Jo6xjZzjwy9QDWMQ

docs/interface/dashboards.md

@@ -240,7 +240,9 @@ A wall tablet has no keyboard, so it pairs.
 
 1. **Dashboards → Panels**, add a panel named after where it hangs, and tick
    the dashboards it shows. More than one and the screen draws a rail to switch
-   between them, with each dashboard's own icon on it.
+   between them, with each dashboard's own icon on it. On a phone the rail is a
+   row floating along the bottom; the app shows it there too, above its own
+   buttons, for a dashboard that hangs on such a panel.
 2. Tick **Touch friendly** if the screen is touched rather than pointed at.
    Controls and the rail grow to a finger's size — the rail gets taller without
    taking a wider column, so the arrangement does not move. It sits here rather