Refine calibration, chase, and spin patterns and add spin test

Increase calibration brightness, update chase to use the new logical ring abstraction, and make spin start from a cleared frame with symmetric arm speed, alongside a dedicated on-device spin test script.

Made-with: Cursor

pico/src/patterns/spin.py

@@ -2,7 +2,7 @@
 
 import utime
 
-SPAN = 10  # LEDs on each side of center (match Grab)
+SPAN = 0  # LEDs on each side of center (match Grab)
 LUT_SIZE = 256  # gradient lookup table entries
 
 
@@ -12,6 +12,9 @@ class Spin:
 
     def run(self, preset):
         strips = self.driver.strips
+
+        self.driver.fill((0, 0, 0))
+        self.driver.show_all()
         active_indices = (0, 4)
         c0 = preset.c[0]
         c1 = preset.c[1]
@@ -58,8 +61,8 @@ class Spin:
                 n = strip.num_leds
                 mid = midpoints[idx]
 
-                # Expand arms: inside (strip 1, idx 0) moves slower, outside (strip 5, idx 4) faster
-                step = max(1, rate // 2) if idx == 0 else rate
+                # Expand arms at the same rate on both sides
+                step = max(1, rate)
                 new_left = max(margin, left[idx] - step)
                 new_right = min(n - margin, right[idx] + step)