Mobs: a mob's particles reach the clients, not a headless buffer

`MobEvent::ParticleAt` was drawn with `self.particles.add` only, and a serving
client has no window: the squid's 30 ink particles never left the server. Send
them as packets like every other server-thread particle site; with count 0 the
packet's deltas are the particle's motion.

Co-Authored-By: Hermes <[email protected]>

crates/horizon-client/src/game/creatures.rs

@@ -2747,6 +2747,21 @@ impl Game<'_> {
                     if let Some(ty) = horizon_client::particles::ParticleType::from_name(kind) {
                         let options = horizon_client::particles::ParticleOptions::simple(ty);
                         self.particles.add(&options, at, velocity);
+                        // A serving client draws nothing on its own: the mob's
+                        // particles have to reach the clients as packets. With
+                        // count 0 the packet's deltas are the particle's motion
+                        // (`ServerLevel.sendParticles` with no spread), which is
+                        // what the event already carries.
+                        self.lan_send_particles(super::lan_particles::QueuedParticle {
+                            dimension: self.dim.id(),
+                            options,
+                            state: None,
+                            at,
+                            spread: velocity,
+                            speed: 0.1,
+                            count: 0,
+                            randomization: 0,
+                        });
                     }
                 }
                 MobEvent::ParticleColored {