Add special caster sparkle effect

context/combat.md

@@ -5,6 +5,7 @@
 - Casters must be living, non-elite, non-magic fighters from teams that are not currently tied for first by represented living count. When `SPECIAL_EFFECT.CASTER.BALANCE_NON_MAGIC_TYPES` is enabled, caster selection first picks among available non-magic types and then picks a fighter from that type, preventing the larger melee roster from overwhelming ranged special casts. If no caster exists at the chosen time, the timer retries within the configured window instead of firing multiple times.
 - Special casters receive realtime invulnerability for `SPECIAL_EFFECT.CASTER.INVULNERABLE_MS`. `combat.js` checks that window in normal attacks, world-effect damage, and special instant kills, while `worldEffects.js` also skips frost survivor effects for invulnerable fighters.
 - While the caster holds the Hurt frame, `specialEffects.js` pauses fighter AI, Arcade Physics, the scene clock, existing combat-object physics velocity, combat-object animations, and combat-object tweens. Existing combat/world delayed calls and already-falling meteor/frost tweens stop advancing until the realtime preparation hold releases into the attack animation.
+- The Hurt-frame preparation also spawns a caster sparkle overlay from `public/assets/effects/special/effect.png`. Its animation uses the 1-based frame sequence `[2, 3, 4]` only, positions near the caster's eyes through `SPECIAL_EFFECT.CASTER_SPARKLE`, and is disposed before the attack animation starts.
 - Caster emphasis uses `SPECIAL_EFFECT.FOCUS_LAYER`: `specialEffects.js` snapshots the current battlefield into a render texture, applies Phaser Blur FX when available, adds a dim layer, and raises the caster above both layers until cleanup.
 - The special camera does not follow the projectile. When projectile movement begins, `zoomOutSpecialEffectCameraFocus()` zooms out in place using `SPECIAL_EFFECT.CAMERA.PROJECTILE_VIEW_ZOOM` and `PROJECTILE_ZOOM_OUT_MS` so the projectile remains readable without dragging the camera off the arena.
 - Melee special projectile effects can define 1-based `frameSequence` arrays. `specialEffects.js` converts them to Phaser frames so the largest frames can be repeated for readability, and melee projectile animations loop while traveling. The projectile's `startHoldMs` keeps it visible at the caster before travel begins.