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/frontend/src/lib/rendered-report.svelte.ts

@@ -37,6 +37,12 @@ export interface RenderedReportSource {
  * underlying `$state` accesses inside `applyOrderOverlay`, so any
  * change to the report or the draft re-runs every dependent
  * `$derived` block.
+ *
+ * Phase 26: the order draft is composed against the *current* turn,
+ * so projecting it onto a historical snapshot would render fictional
+ * intent on a past report. In history mode the getter returns the
+ * raw server snapshot untouched — the order tab is hidden anyway and
+ * mutations are gated at the store, so nothing else needs to know.
  */
 export function createRenderedReportSource(
 	gameState: GameStateStore,
@@ -46,6 +52,7 @@ export function createRenderedReportSource(
 		get report(): GameReport | null {
 			const raw = gameState.report;
 			if (raw === null) return null;
+			if (gameState.historyMode) return raw;
 			return applyOrderOverlay(raw, orderDraft.commands, orderDraft.statuses);
 		},
 	};