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_003_blue_sparkle.h

@@ -0,0 +1,15 @@
+// Generated by convert_all.py from: 003_blue_sparkle.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_003_BLUE_SPARKLE[] PROGMEM = {
+    {  5,   0,  24,     0},  // #050018, 0ms
+    { 32,  32, 255,  2500},  // #2020FF, 2500ms
+    { 32,  32, 255,   400},  // #2020FF, 400ms
+    {  5,   0,  24,  2500},  // #050018, 2500ms
+    {  5,   0,  24,   800},  // #050018, 800ms
+};
+const uint16_t SHOW_003_BLUE_SPARKLE_LENGTH = 5;