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

frontend/src/routes/panel.$id.tsx

@@ -21,7 +21,7 @@ import { cn } from "@/lib/utils"
  * What a paired device shows: the dashboards this panel was assigned.
  *
  * The same full-bleed surface as `/view/{name}`, with a rail down the left
- * when there is more than one to switch between — so a hallway tablet and a
+ * (along the bottom on a phone) when there is more than one to switch between — so a hallway tablet and a
  * workshop tablet can carry different sets without either dashboard knowing
  * anything about the other.
  *
@@ -112,6 +112,7 @@ function PanelRoute() {
                 <PanelRail
                   dashboards={dashboards}
                   current={current}
+                  horizontal={stacked}
                   linkFor={(name) => ({
                     to: "/panel/$id",
                     params: { id },