ui/phase-26: history mode (turn navigator + read-only banner)

Split GameStateStore into currentTurn (server's latest) and viewedTurn
(displayed snapshot) so history excursions don't corrupt the resume
bookmark or the live-turn bound. Add viewTurn / returnToCurrent /
historyMode rune, plus a game-history cache namespace that stores
past-turn reports for fast re-entry. OrderDraftStore.bindClient takes
a getHistoryMode getter and short-circuits add / remove / move while
the user is viewing a past turn; RenderedReportSource skips the order
overlay in the same case. Header replaces the static "turn N" with a
clickable triplet (TurnNavigator), the layout mounts HistoryBanner
under the header, and visibility-refresh is a no-op while history is
active.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/docs/order-composer.md

@@ -300,13 +300,14 @@ order composer uses the namespace.
 
 ## History mode wiring
 
-Phase 26 introduces a global history-mode flag. The IA section
-specifies that the Order tab is hidden when history mode is active —
-the player is browsing a past turn snapshot, and composing commands
-against an immutable snapshot would be confusing.
+Phase 26 implements history mode: the user can step back through
+past turns and see the report as it was. The IA section specifies
+that the Order tab is hidden when history mode is active — the
+player is browsing an immutable snapshot, and composing commands
+against it would be confusing.
 
 Phase 12 wires the flag end-to-end as a prop. The layout owns the
-flag (a constant `false` until Phase 26) and passes it to:
+flag and passes it to:
 
 - `Sidebar` as `historyMode`. The sidebar forwards it to its
   `TabBar` as `hideOrder`. The Order entry is filtered out of the
@@ -317,10 +318,31 @@ flag (a constant `false` until Phase 26) and passes it to:
 - `BottomTabs` as `hideOrder`. The mobile bottom-tab `Order`
   button is suppressed when true.
 
+Phase 26 turns the constant into a derived value driven by
+`GameStateStore.historyMode` (`viewedTurn < currentTurn` while
+`status === "ready"`). The same getter is also passed into
+`OrderDraftStore.bindClient` as `getHistoryMode`, which short-
+circuits the `add` / `remove` / `move` mutations to a no-op while
+the flag is true. This makes every Phase 14–22 inspector affordance
+that calls `orderDraft.add(...)` inert in history mode without
+per-component edits — the gate lives in the one chokepoint that
+all callers go through. The conflict / paused banners and the
+in-flight sync pipeline are untouched: they describe state that
+exists independently of the user's current view.
+
 The store itself stays alive across history-mode round-trips so
-the draft survives. Phase 26 will replace the constant with the
-real signal from `lib/history-mode.ts` and exercise the toggle in
-its own test suite.
+the draft survives the toggle. The `RenderedReportSource` overlay
+(`lib/rendered-report.svelte.ts`) additionally short-circuits in
+history mode: when `gameState.historyMode === true` it returns
+the raw report so the map / inspector do not project pending
+renames composed for the *current* turn onto a *past* report.
+
+See [`game-state.md`](game-state.md) for the `viewTurn` /
+`returnToCurrent` API, the cache namespace
+(`game-history/{gameId}/turn/{N}`), and the visibility-refresh
+short-circuit; see [`navigation.md`](navigation.md) for the turn
+navigator and the read-only banner that surface history mode in
+the chrome.
 
 ## Testing