ui/phase-27: mass-based circles + cloud cluster + height fit

Three Phase-27 BattleViewer refinements on top of the radial scene:

1. Height fit. The viewer is pinned to `calc(100dvh − 80px)` so it
   never pushes the in-game shell past the viewport. `.active-view`
   gains `overflow: hidden` + flex column; `.viewer` becomes a
   `flex: 1` child; the always-visible text log shrinks to a 30 dvh
   ceiling with its own scroll. A global `body { margin: 0 }`
   reset (added to `app.html`) plugs the 16 px the browser's
   default body margin used to leak.

2. Mass-based ship-class circles. New `lib/battle-player/mass.ts`
   carries the radius formula and the per-battle FullMass compute:
   `MIN_RADIUS + (MAX_RADIUS − MIN_RADIUS) * sqrt(mass / max)`,
   clamped to `[6, 24] px`. FullMass goes through the existing
   wasm bridge (`emptyMass` → `carryingMass` → `fullMass`) — no
   new wire fields. The viewer page resolves a
   `(race, className) → ShipClassRef` lookup from the parent
   GameReport's `localShipClass` + `otherShipClass` tables and
   passes it to the viewer via context. Unknown class or
   degenerate (weapons/armament) params fall back to MAX_RADIUS
   so the bucket stays visible.

3. Cloud cluster layout. Cluster key shifts from per-group
   `g.key` to `(raceId, className)` so tech-variants of the same
   hull collapse into one visual bucket. The horizontal
   classCircleX row is replaced by a Vogel sunflower spiral in
   the local `(u, v)` basis — `u` points from the race anchor to
   the planet, `v` is `u` rotated 90° clockwise. Buckets are
   sorted by NumberLeft desc; the cluster anchor is pushed inward
   by a quarter step so rank-0 sits closest to the planet. The
   step is adaptive (`min(baseStep, MAX_CLUSTER_RADIUS / sqrt(N))`)
   so clusters with many classes do not spill into neighbours.

Tests:
- Vitest: `radiusForMass` covering zero / max / quarter-mass /
  out-of-range cases (6 cases).
- Playwright: new `battle-viewer.spec.ts` case asserts
  `document.documentElement.scrollHeight - window.innerHeight ≤ 4`
  at a 1280×720 desktop viewport. The existing fixture gains
  `localShipClass` + `otherShipClass` so the lookup has data to
  render proportional circles.

Docs: `ui/docs/battle-viewer-ux.md` rewrites the "Radial scene"
section (cloud layout, mass-based radius, height fit) and adds
a "Height fit" subsection. `docs/FUNCTIONAL.md` §6.5 (+ ru
mirror) get the one-line story about per-mass sizing, cluster
aggregation, and the viewport-locked layout.

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

ui/frontend/tests/e2e/battle-viewer.spec.ts

@@ -129,6 +129,28 @@ async function mockGatewayAndBattle(page: Page): Promise<void> {
 							},
 						],
 						battles: [{ id: BATTLE_ID, planet: 1, shots: 4 }],
+						localShipClass: [
+							{
+								name: "Cruiser",
+								drive: 10,
+								armament: 2,
+								weapons: 5,
+								shields: 5,
+								cargo: 2,
+							},
+						],
+						otherShipClass: [
+							{
+								race: "Bajori",
+								name: "Hawk",
+								drive: 12,
+								armament: 1,
+								weapons: 4,
+								shields: 2,
+								cargo: 0,
+								mass: 75,
+							},
+						],
 					});
 					break;
 				}
@@ -249,4 +271,35 @@ test.describe("Phase 27 battle viewer", () => {
 
 		await expect(page.getByTestId("battle-not-found")).toBeVisible();
 	});
+
+	test("viewer fits the desktop viewport without a vertical scroll", async ({
+		page,
+	}, testInfo) => {
+		test.skip(
+			testInfo.project.name.startsWith("chromium-mobile"),
+			"desktop-only height-fit check",
+		);
+
+		await page.setViewportSize({ width: 1280, height: 720 });
+		await mockGatewayAndBattle(page);
+		await bootSession(page);
+		await page.goto(`/games/${GAME_ID}/battle/${BATTLE_ID}?turn=1`);
+
+		await expect(page.getByTestId("battle-viewer")).toBeVisible();
+		await expect(page.getByTestId("battle-scene")).toBeVisible();
+
+		// Phase 27 refinement: viewer + log fit the viewport; the
+		// internal log scrolls inside its own pane rather than
+		// growing the page. Allow a small tolerance for fractional
+		// pixel rounding around flex math, but reject any
+		// scrollable overflow beyond a couple of pixels.
+		// Phase 27 refinement: viewer + log fit the viewport; the
+		// internal log scrolls inside its own pane rather than
+		// growing the page. Allow a small tolerance for fractional
+		// pixel rounding around flex math.
+		const overflow = await page.evaluate(
+			() => document.documentElement.scrollHeight - window.innerHeight,
+		);
+		expect(overflow).toBeLessThanOrEqual(4);
+	});
 });