ui/phase-27: viewer layout pass + static cluster + duel layout

Layout reshuffle so the scene captures the maximum viewer area:

- Header collapses three rows into one: `back to map` / `back to
  report` on the left, the centred title `Battle on planet <name>
  (#<number>)` (new i18n key `game.battle.header_title`), and the
  frame counter on the right. The wrapper `.active-view` no longer
  renders its own back-row; routes flow through props.
- Viewer drops the `max-width: 880px` cap so on a wide monitor the
  scene scales up across the full active-view-host.
- A drag-seek `<input type="range">` sits between the scene and the
  controls; dragging pauses playback and lands `frameIndex` on the
  chosen shot.
- Speed control is one cycling button: `1x → 2x → 4x → 6x → 1x`.
  The label shows the current speed; the new 6x adds a 67 ms frame
  interval for skimming a long timeline.
- The text protocol log is now collapsible behind a `Log ▲▼`
  toggle in the controls bar. The toggle is its own button; the
  default state stays expanded. Collapsing the log hands the
  remaining height to the scene.
- Numerical list markers (`1. 2. 3.`) are dropped from the log;
  `list-style: none` keeps each row visually clean.

Static cluster + visibility filter:

- `staticBucketsByRace` now locks bucket order, mass, radius and
  local Vogel-spiral positions for the lifetime of the viewer; it
  only re-derives when `report` or the wasm `core` change.
- `renderedByRace` overlays the per-frame `remaining` map and drops
  buckets whose `numLeft` hits zero. The surviving buckets keep
  their slots, so a class emptying never reshuffles the cluster —
  the empty bucket simply disappears.
- A shot whose attacker or defender bucket is no longer visible
  draws no line (phantom shots into already-empty buckets are
  silently skipped, matching the user expectation that pup at 0
  should stop attracting fire visually).
- Race label clamps to a minimum y inside the SVG viewport so
  three-or-more-race layouts with a north anchor never clip the
  top race name off-canvas.

Duel layout (user suggestion):

- `layoutRaces` rotates the radial start angle by 90° when only
  two participants remain, so race 0 lands at 9 o'clock and race 1
  at 3 o'clock. The pair faces off horizontally; neither label
  pushes against the SVG top edge. The existing test for two-race
  positions is updated accordingly.

Tests: the existing `layoutRaces` two-race case is rewritten for
the horizontal duel; the `game-shell-stubs` battle case checks the
loading placeholder (back buttons now live in the loaded viewer,
not the wrapper). 644 Vitest cases stay green; 4 Playwright
battle-viewer cases stay green.

Docs: `ui/docs/battle-viewer-ux.md` documents the static cluster /
visibility filter, the duel layout, the scrubber, the cycling
speed button and the collapsible log.

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

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

@@ -76,20 +76,20 @@ describe("active-view stubs", () => {
 		);
 	});
 
-	test("battle view stamps the battleId and renders the back-to-map link", () => {
+	test("battle view stamps the battleId and shows the loading placeholder", () => {
 		// 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.
+		// wrapper. The latest layout iteration moved the back-
+		// navigation buttons inside `BattleViewer` so they only mount
+		// once the BattleReport finishes loading. The wrapper itself
+		// always renders the `active-view-battle` host with the
+		// `data-battle-id` stamp and a localized loading copy until
+		// the fetcher resolves.
 		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(ui.getByTestId("battle-back-to-map")).toBeInTheDocument();
-		expect(ui.getByTestId("battle-back-to-report")).toBeInTheDocument();
+		expect(ui.getByTestId("battle-loading")).toBeInTheDocument();
 	});
 
 	test("battle view surfaces the not-found state for an empty battleId", () => {