feat(game): race exit warnings in the turn report (#12)

Surface the inactivity-removal countdown the rules promise but the
engine never reported. A race within five turns of being auto-removed
for inactivity gets a personal warning in its own report; every race
within three turns is listed publicly to all participants.

- model: Report.PersonalExitWarning + RacesLeavingSoon ([]RaceExitNotice)
- fbs: RaceExitNotice table + Report.personal_exit_warning /
  races_leaving_soon (regenerated Go + TS bindings)
- transcoder: encode/decode both fields
- engine: ReportExitWarnings fills the recipient's TTL (1..5) and lists
  other non-extinct races with TTL 1..3, excluding the recipient itself
- ui: danger-styled personal banner + "races leaving soon" section
  (hidden when empty), wired into the report view, EN/RU i18n
- docs: rules.txt report-section list, FUNCTIONAL.md 6.4 + RU mirror

Voluntary quit and idle timeout share the TTL countdown and are not
distinguished, per the agreed scope.

ui/frontend/src/api/synthetic-report.ts

@@ -9,6 +9,14 @@
 // AND the Go CLI must learn to populate that field — see the
 // synthetic-report parity rule in `ui/PLAN.md`.
 //
+// `personalExitWarning` / `racesLeavingSoon` are the exception the
+// rule allows: they are runtime inactivity-countdown state the engine
+// derives per turn, not anything present in a static legacy text
+// report, so the legacy CLI leaves them empty (the parity rule's
+// "cannot be derived from the legacy text format" escape hatch). This
+// decoder still reads them defensively so a hand-authored synthetic
+// JSON fixture can exercise the report's exit-warning UI.
+//
 // The in-memory map deliberately does not survive a page reload:
 // synthetic mode is a debug affordance, not a session, and the
 // layout redirects to /lobby when a synthetic id is opened with no
@@ -259,6 +267,11 @@ interface SyntheticShipProductionRow {
 	free?: number;
 }
 
+interface SyntheticRaceExitNotice {
+	race?: string;
+	turnsLeft?: number;
+}
+
 interface SyntheticReportRoot {
 	turn?: number;
 	mapWidth?: number;
@@ -284,6 +297,8 @@ interface SyntheticReportRoot {
 	battle?: SyntheticBattle[];
 	bombing?: SyntheticBombing[];
 	shipProduction?: SyntheticShipProductionRow[];
+	personalExitWarning?: number;
+	racesLeavingSoon?: SyntheticRaceExitNotice[];
 }
 
 function decodeSyntheticReport(json: unknown): GameReport {
@@ -465,6 +480,13 @@ function decodeSyntheticReport(json: unknown): GameReport {
 		return a.class.localeCompare(b.class);
 	});
 
+	const racesLeavingSoon: { race: string; turnsLeft: number }[] = (
+		root.racesLeavingSoon ?? []
+	).map((n) => ({
+		race: typeof n.race === "string" ? n.race : "",
+		turnsLeft: numOr0(n.turnsLeft),
+	}));
+
 	return {
 		turn: numOr0(root.turn),
 		mapWidth: numOr0(root.mapWidth),
@@ -495,6 +517,8 @@ function decodeSyntheticReport(json: unknown): GameReport {
 		battleIds,
 		bombings,
 		shipProductions,
+		personalExitWarning: numOr0(root.personalExitWarning),
+		racesLeavingSoon,
 	};
 }