Replace example shows with numbered production shows and add sparkle flag

- Rename all show .txt files with NNN_ numeric prefix so order is explicit
  and controlled by filename (001_heartbeat_red through 006_party)
- Drop HOME_SHOW special-casing from convert_all.py; show 0 is simply the
  lowest-numbered file
- Add SHOW_FLAG_SPARKLE support: shows can declare '// flags: sparkle' to
  overlay random white flashes on top of the base color each frame
- Wire sparkle into led_controller and config.h (SPARKLE_CHANCE/FRAMES)
- Replace old placeholder/example shows with the six production shows

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

arduino/cosplay_lights/led_controller.h

@@ -7,8 +7,9 @@
 void leds_begin();
 
 // Apply 'color' to all LEDs using the pattern defined in config.h (ACTIVE_PATTERN).
+// If 'sparkle' is true, randomly flash individual LEDs white on top of the base fill.
 // Call leds_show() afterwards to push the update to the physical strip.
-void leds_apply_color(CRGB color);
+void leds_apply_color(CRGB color, bool sparkle = false);
 
 // Flush the LED buffer to the physical strip. Call once per frame after leds_apply_color().
 void leds_show();