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/show_002_heartbeat_breathe.h

@@ -0,0 +1,12 @@
+// Generated by convert_all.py from: 002_heartbeat_breathe.txt
+// Do not edit manually — edit the .txt file and run: make shows
+// SPDX-License-Identifier: BSD-2-Clause
+
+#pragma once
+#include "lightshow_format.h"
+
+const Step SHOW_002_HEARTBEAT_BREATHE[] PROGMEM = {
+    {209,  14,  41,  3600},  // #D10E29, 3600ms
+    {  5,   0,   0,  3600},  // #050000, 3600ms
+};
+const uint16_t SHOW_002_HEARTBEAT_BREATHE_LENGTH = 2;