fix: remove collision_delay to eliminate movement deadlock

collision_delay was causing entities to skip step_recovery ticks, freezing
movement whenever the next tile was occupied. Combined with the ordering fix
(collision_delay placed before step_recovery), entities were stuck at
path_index=0 indefinitely in spawn clusters.

Remove collision_delay entirely — step_recovery already provides the
per-tick pacing, and the natural next-tick retry (via left-step or
normal movement) handles occupied tiles without an artificial delay.

Actual thresholds (grass weight=50): dorfs move after 6 ticks, pigs after
26 ticks, rabbits after 2 ticks. Without collision_delay interference,
movement is now governed purely by step_recovery.

src/entities/livestock/rabbit.rs

@@ -27,7 +27,6 @@ impl Rabbit {
                 path_index: 0,
                 step_recovery: 0,
                 validation_cooldown: 0,
-                collision_delay: 0,
             },
             sprite: Sprite {
                 image: asset_server.load("rabbit.png"),