ui/phase-27: battle viewer (radial scene, playback, map markers)

Engine wire change: Report.battle switched from []uuid.UUID to
[]BattleSummary{id, planet, shots} so the map can place battle
markers without N extra fetches. FBS schema + generated Go/TS
regenerated; transcoder + report controller updated; openapi
adds the BattleSummary schema with a freeze test.

Backend gateway forwards engine GET /api/v1/battle/:turn/:uuid as
/api/v1/user/games/{game_id}/battles/{turn}/{battle_id} (handler
plus engineclient.FetchBattle, contract test stub, openapi spec).

UI:
- BattleViewer (lib/battle-player/) is a logically isolated SVG
  radial scene that consumes a BattleReport prop. Planet at the
  centre, races on the outer ring at equal angular spacing, race
  clusters by (race, className) with <class>:<numLeft> labels;
  observer groups (inBattle: false) are not drawn; eliminated
  races drop out and survivors re-distribute on the next frame.
- Shot line per frame: red on destroyed, green otherwise; erased
  on the next frame. Playback controls: play/pause + step ± +
  rewind + 1x/2x/4x speed (400/200/100 ms per frame).
- Page wrapper (lib/active-view/battle.svelte) loads BattleReport
  via api/battle-fetch.ts; synthetic-gameId prefix routes to a
  fixture loader, otherwise REST through the gateway. Always-
  visible <ol> text protocol satisfies the accessibility ask.
- section-battles.svelte links every battle UUID into the viewer.
- map/battle-markers.ts: yellow X cross of 2 LinePrim through the
  corners of the planet's circumscribed square (stroke width
  clamps from 1 px at 1 shot to 5 px at 100+ shots); bombing
  marker is a stroke-only ring (yellow when damaged, red when
  wiped). Wired into state-binding.ts; click handler dispatches
  battle clicks to the viewer and bombing clicks to the matching
  Reports row.
- i18n keys for the viewer in en + ru.

Docs: ui/docs/battle-viewer-ux.md, FUNCTIONAL.md §6.5 + ru
mirror, ui/PLAN.md Phase 27 decisions + deferred TODOs (push
event, richer class visuals, animated re-distribution).

Tests: Vitest unit (radial layout + timeline frame builder +
marker stroke formula + marker primitives), Playwright e2e for
the viewer (Reports link → viewer, playback step, not-found),
backend engineclient FetchBattle (200 / 404 / bad input), engine
openapi freezes (BattleReport, BattleReportGroup,
BattleActionReport, BattleSummary, Report.battle items).

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

ui/frontend/tests/game-shell-stubs.test.ts

@@ -76,18 +76,30 @@ describe("active-view stubs", () => {
 		);
 	});
 
-	test("battle stub stamps the battleId on the host element", () => {
-		const ui = render(BattleView, { props: { battleId: "b-42" } });
+	test("battle view stamps the battleId and renders the back-to-map link", () => {
+		// Phase 27 replaces the Phase 10 stub with the Battle Viewer
+		// wrapper. The wrapper mounts the loading copy until the
+		// fetcher resolves (component test runs in jsdom without a
+		// network); the back buttons and the data-battle-id stamp are
+		// rendered unconditionally so the orchestrator scaffold is the
+		// stable hook the active-view shell relies on.
+		const ui = render(BattleView, {
+			props: { gameId: "synthetic-test", turn: 0, battleId: "b-42" },
+		});
 		const node = ui.getByTestId("active-view-battle");
 		expect(node).toHaveAttribute("data-battle-id", "b-42");
-		expect(node).toHaveTextContent("battle log");
+		expect(ui.getByTestId("battle-back-to-map")).toBeInTheDocument();
+		expect(ui.getByTestId("battle-back-to-report")).toBeInTheDocument();
 	});
 
-	test("battle stub accepts an empty battleId for the list URL", () => {
-		const ui = render(BattleView, { props: { battleId: "" } });
+	test("battle view surfaces the not-found state for an empty battleId", () => {
+		const ui = render(BattleView, {
+			props: { gameId: "synthetic-test", turn: 0, battleId: "" },
+		});
 		expect(ui.getByTestId("active-view-battle")).toHaveAttribute(
 			"data-battle-id",
 			"",
 		);
+		expect(ui.getByTestId("battle-not-found")).toBeInTheDocument();
 	});
 });