Enemies no longer attack; add a fixed bullet-ring emitter and make lasers permanent obstacles

walker.gd lost its firing code entirely: monsters now only patrol and hurt on contact, so the only way past is footwork or the key throw + W warp. New bullet_ring prefab fires a set number of bullets evenly spread over a fixed arc on a timer, with directions derived only from its own exports, so every volley is identical and the pattern can be memorised; the level places one at cell (12,12) aimed upward with the 12 bullets spread over 180 degrees. laser.gd gained always_on, defaulting to true, so the five copied lasers are now static hazards that are always lit and damage anything overlapping them rather than blinking on and off. Bullets now stop when they spawn inside terrain.

scripts/bullet.gd.uid

@@ -0,0 +1 @@
+uid://c4v4jls42gsyk