ui/phase-12: order composer skeleton

OrderDraftStore persists per-game command drafts in Cache; the
sidebar Order tab renders the list with a per-row delete control.
The layout passes a `historyMode` prop through Sidebar / BottomTabs
as a constant `false`, so Phase 26 only flips the source.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/docs/navigation.md

@@ -61,6 +61,20 @@ on mount and seeds the initial tab. Later phases that want to land
 the user on a particular tool (for example, Phase 14's first
 end-to-end command flow) can set it on navigation.
 
+The Order entry is hidden when the layout's `historyMode` flag is
+true. Phase 12 plumbs the flag end-to-end as a prop —
+`+layout.svelte` passes a constant `false` to `Sidebar`, which
+forwards `hideOrder` to its `TabBar`; the same flag goes to
+`BottomTabs` so the mobile `Order` button is also suppressed. A
+`?sidebar=order` URL seed that arrives while the flag is true falls
+back to `inspector`, and an `$effect` on the sidebar resets
+`activeTab` away from `order` if the flag flips on mid-session.
+Phase 26 introduces `lib/history-mode.ts` and replaces the constant
+with the live signal; the order draft survives the toggle because
+`OrderDraftStore` lives one level above the sidebar in the layout
+hierarchy. See [`order-composer.md`](order-composer.md) for the
+draft-store side of the flow.
+
 ## Layout breakpoints
 
 Three discrete CSS modes matched to the IA section diagrams: