fix(patterns): use preset background fallback across animations

Align pattern background rendering to use preset.background_or(...) and update pulse/radiate single-step behaviour to preserve visible frames and step progression.

src/patterns/pulse.py

@@ -6,19 +6,19 @@ class Pulse:
         self.driver = driver
 
     def run(self, preset):
-        self.driver.off()
-
         # Get colors from preset
         colors = preset.c
         if not colors:
             colors = [(255, 255, 255)]
+        bg_base = preset.background_or(colors)
+        self.driver.fill(self.driver.apply_brightness(bg_base, preset.b))
 
-        color_index = 0
+        color_index = self.driver.step % max(1, len(colors))
         cycle_start = utime.ticks_ms()
 
         # State machine based pulse using a single generator loop
         while True:
-            bg_color = self.driver.apply_brightness(colors[-1], preset.b)
+            bg_color = self.driver.apply_brightness(bg_base, preset.b)
             # Read current timing parameters from preset
             attack_ms = max(0, int(preset.n1))  # Attack time in ms
             hold_ms = max(0, int(preset.n2))    # Hold time in ms
@@ -53,7 +53,8 @@ class Pulse:
                 self.driver.fill(bg_color)
             else:
                 # End of cycle, move to next color and restart timing
-                color_index += 1
+                color_index = (color_index + 1) % max(1, len(colors))
+                self.driver.step = color_index
                 cycle_start = now
                 if not preset.a:
                     break