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/cosplay_lights.ino

@@ -6,7 +6,7 @@
  *   1 tap  — next show
  *   2 taps — previous show
  *   3 taps — lights off (any tap or hold resumes)
- *   hold   — reset to show 0 (blue breath)
+ *   hold   — reset to show 0 (red heartbeat)
  *
  * To add or update shows:
  *   1. Add or edit a .txt file in converter/shows/
@@ -79,7 +79,7 @@ void setup() {
     s_button.setPressMs(800);
     s_button.attachClick([]()          { load_show((s_show_index + 1) % SHOW_COUNT); });
     s_button.attachDoubleClick([]()    { load_show((s_show_index + SHOW_COUNT - 1) % SHOW_COUNT); });
-    s_button.attachMultiClick([]()     { if (s_button.getNumberClicks() == 3) { s_lights_off = true; leds_apply_color(CRGB::Black); leds_show(); } });
+    s_button.attachMultiClick([]()     { if (s_button.getNumberClicks() == 3) { s_lights_off = true; leds_apply_color(CRGB::Black, false); leds_show(); } });
     s_button.attachLongPressStart([]() { load_show(0); });
 }
 
@@ -97,7 +97,8 @@ void loop() {
     CRGB    to   = CRGB(step.r, step.g, step.b);
     uint8_t t8   = step_progress(step, now);
 
-    leds_apply_color(blend(s_from_color, to, t8));
+    bool sparkle = (s_show.flags & SHOW_FLAG_SPARKLE) != 0;
+    leds_apply_color(blend(s_from_color, to, t8), sparkle);
     leds_show();
 
     if (t8 == 255) advance_step(to, now);