feat: sparkles nuke-explosion visual type (#4490)

## Description:

Follow-up to #4485: adds a second nuke-explosion visual, `"sparkles"` —
a firework burst of twinkling glints that start at the detonation point
and ride outward with the expanding front, reaching the cosmetic's full
`size` at fade-out.

**Schema (`CosmeticSchemas.ts`)**
- `NukeExplosionAttributesSchema` is now a discriminated union on `type`
(`"shockwave" | "sparkles"`), matching `TrailEffectAttributesSchema`.
Old clients drop sparkles entries via `lenientRecord` and render the
default ring.
- The sparkles member adds `density` (required, positive) — roughly the
total number of glints in the burst.
- Literal attribute semantics, consistent with shockwave:
  - `size` — final burst width (diameter) in world tiles at fade-out
- `speed` — tiles/s the width grows; duration = size / speed, clamped
0.1–15 s
- `thickness` — **average** sparkle size in tiles; each glint
hash-varies ±50% around it
  - `density` — approximate glint count; renderer clamps to 2–5000
- `colors` + `transitionSpeed` — shared palette-cycle semantics, with a
hashed per-glint palette offset on top

**Rendering**
- `NukeExplosionRenderParams` now carries the visual type through to the
pass as a matching TS union (previously any cosmetic was hardwired to
the EMP style — this closes that gap for future visuals).
- Sparkles are style 2 in the same `FxShockwavePass` instance stream:
one new float (grid cell pitch, derived CPU-side from density), no other
layout changes.
- Fragment shader: one hashed glint per rotated front-normalized grid
cell (jittered, cell-confined so each fragment samples only its own
cell, ~1/3 dropout for organic scatter), hashed birth stagger. Glints
are **fully opaque** — twinkle modulates color brightness, not alpha —
holding full opacity through life and fading only over the last quarter.
- SAM interceptions, the classic ring, and EMP shockwaves are unchanged.

**Store / selection**
- New `<sparkles-swatch>` preview (burst scales from center,
density-scaled dot count, size-varied dots, palette cycling), branched
in `CosmeticButton` by `attributes.type`.

**Verification**
- Schema tests incl. the real `rgb_nuke_sparkles` catalog entry,
missing/non-positive `density` rejection.
- Verified in-game via headless Chromium: size-250 RGB burst renders
opaque red/white/blue glints expanding from the detonation point; sparse
(40) vs dense (400) density comparison; no page errors.

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/client/WebGLFrameBuilder.ts

@@ -81,13 +81,16 @@ function attributesToExplosionParams(
     .map(toRgb01)
     .filter((c): c is [number, number, number] => c !== null)
     .slice(0, MAX_NUKE_EXPLOSION_COLORS);
-  return {
+  const base = {
     colors: colors.length > 0 ? colors : [DEFAULT_NUKE_EXPLOSION_COLOR],
     maxRadius: attrs.size / 2,
     speed: attrs.speed,
     thickness: attrs.thickness,
     transitionSpeed: attrs.transitionSpeed,
   };
+  return attrs.type === "sparkles"
+    ? { ...base, type: "sparkles", density: attrs.density }
+    : { ...base, type: "shockwave" };
 }
 
 /**