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/i18n/locales/en.ts

@@ -89,7 +89,6 @@ const en = {
 	"lobby.error.unknown": "{message}",
 
 	"game.shell.unknown": "?",
-	"game.shell.headline": "{race} @ {game}, turn {turn}",
 	"game.shell.connection.online": "online",
 	"game.shell.connection.reconnecting": "reconnecting…",
 	"game.shell.connection.offline": "offline",
@@ -104,6 +103,15 @@ const en = {
 	"game.shell.menu.language": "language",
 	"game.shell.menu.logout": "logout",
 	"game.shell.coming_soon": "coming soon",
+	"game.shell.turn.label": "turn {turn}",
+	"game.shell.turn.list_item": "turn #{turn}",
+	"game.shell.turn.prev": "previous turn",
+	"game.shell.turn.next": "next turn",
+	"game.shell.turn.open_navigator": "open turn list",
+	"game.shell.turn.close_navigator": "close turn list",
+	"game.shell.history.viewing": "Viewing turn {turn} · read-only",
+	"game.shell.history.return_to_current": "Return to current turn",
+	"game.shell.history.current_badge": "current",
 	"game.view.map": "map",
 	"game.view.table": "table",
 	"game.view.table.planets": "planets",