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/battle-player.test.ts

@@ -34,13 +34,16 @@ describe("layoutRaces", () => {
 		expect(result[0].y).toBeCloseTo(center.y - radius, 5);
 	});
 
-	it("places two races at opposite poles (180° apart)", () => {
+	it("places two races on the horizontal axis (9 vs 3 o'clock)", () => {
+		// Special-case duel layout: two anchors face each other on
+		// the horizontal axis so neither cluster's race label clips
+		// against the SVG top edge.
 		const result = layoutRaces([0, 1], { center, radius });
 		expect(result).toHaveLength(2);
-		expect(result[0].x).toBeCloseTo(center.x, 5);
-		expect(result[0].y).toBeCloseTo(center.y - radius, 5);
-		expect(result[1].x).toBeCloseTo(center.x, 5);
-		expect(result[1].y).toBeCloseTo(center.y + radius, 5);
+		expect(result[0].x).toBeCloseTo(center.x - radius, 5);
+		expect(result[0].y).toBeCloseTo(center.y, 5);
+		expect(result[1].x).toBeCloseTo(center.x + radius, 5);
+		expect(result[1].y).toBeCloseTo(center.y, 5);
 	});
 
 	it("places three races at 120° intervals", () => {