fix(patterns): correct non-blocking timing and blink off phase

Co-authored-by: Cursor <cursoragent@cursor.com>

src/patterns/clock_sweep.py

@@ -15,7 +15,7 @@ class ClockSweep:
             d = max(1, int(preset.d))
             now = utime.ticks_ms()
             if utime.ticks_diff(now, last) >= d:
-                bg = self.driver.apply_brightness(colors[1] if len(colors) > 1 else (0, 0, 0), preset.b)
+                bg = self.driver.apply_brightness(colors[-1], preset.b)
                 fg = self.driver.apply_brightness(colors[0], preset.b)
                 for i in range(self.driver.num_leds):
                     self.driver.n[i] = bg