ui/phase-25: backend turn-cutoff guard + auto-pause + UI sync protocol

Backend now owns the turn-cutoff and pause guards the order tab
relies on: the scheduler flips runtime_status between
generation_in_progress and running around every engine tick, a
failed tick auto-pauses the game through OnRuntimeSnapshot, and a
new game.paused notification kind fans out alongside
game.turn.ready. The user-games handlers reject submits with
HTTP 409 turn_already_closed or game_paused depending on the
runtime state.

UI delegates auto-sync to a new OrderQueue: offline detection,
single retry on reconnect, conflict / paused classification.
OrderDraftStore surfaces conflictBanner / pausedBanner runes,
clears them on local mutation or on a game.turn.ready push via
resetForNewTurn. The order tab renders the matching banners and
the new conflict per-row badge; i18n bundles cover en + ru.

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

backend/internal/runtime/errors.go

@@ -42,4 +42,23 @@ var (
 	// ErrShutdown means the runtime service has stopped accepting
 	// work because the parent context was cancelled.
 	ErrShutdown = errors.New("runtime: shutting down")
+
+	// ErrTurnAlreadyClosed reports that the runtime is currently
+	// producing a turn — runtime status is `generation_in_progress`
+	// — and the engine is not accepting writes for the closing
+	// turn. Handlers map this to HTTP 409 with httperr code
+	// `turn_already_closed`; the UI shows a conflict banner and
+	// waits for the next `game.turn.ready` push.
+	ErrTurnAlreadyClosed = errors.New("runtime: turn already closed")
+
+	// ErrGamePaused reports that the game is not in a state that
+	// accepts user-games commands or orders: the runtime row
+	// carries `paused = true`, or the runtime status lands on any
+	// terminal value (`engine_unreachable`, `generation_failed`,
+	// `stopped`, `finished`, `removed`), or the game has not yet
+	// finished bootstrapping (`starting`). Handlers map this to
+	// HTTP 409 with httperr code `game_paused`; the UI surfaces a
+	// pause banner and waits for an admin resume or a fresh
+	// snapshot.
+	ErrGamePaused = errors.New("runtime: game paused")
 )