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/tests/synthetic-report.test.ts

@@ -189,6 +189,25 @@ describe("loadSyntheticReportFromJSON", () => {
 		expect(report.routes).toEqual([]);
 	});
 
+	test("defaults exit warnings to empty (legacy format has no exit data)", () => {
+		const { report } = loadSyntheticReportFromJSON(syntheticJSON());
+		expect(report.personalExitWarning).toBe(0);
+		expect(report.racesLeavingSoon).toEqual([]);
+	});
+
+	test("reads hand-authored exit warnings when present", () => {
+		const { report } = loadSyntheticReportFromJSON(
+			syntheticJSON({
+				personalExitWarning: 4,
+				racesLeavingSoon: [{ race: "Monstrai", turnsLeft: 2 }],
+			}),
+		);
+		expect(report.personalExitWarning).toBe(4);
+		expect(report.racesLeavingSoon).toEqual([
+			{ race: "Monstrai", turnsLeft: 2 },
+		]);
+	});
+
 	test("registers the report under the returned game id", () => {
 		const { gameId, report } = loadSyntheticReportFromJSON(syntheticJSON());
 		expect(getSyntheticReport(gameId)).toBe(report);