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/lightshow_format.h

@@ -16,6 +16,9 @@
 #define SHOW_LOOP   0  // repeat the show indefinitely
 #define SHOW_SINGLE 1  // play once, then auto-advance to the next show
 
+// Show flags (bitfield for ShowDef.flags).
+#define SHOW_FLAG_SPARKLE 0x01  // overlay random white sparkles on this show
+
 // One step in a lightshow: a target color and the time to reach it.
 struct Step {
     uint8_t  r, g, b;        // Target RGB color (0–255 each)
@@ -27,6 +30,7 @@ struct ShowDef {
     const Step* steps;    // Pointer to a PROGMEM Step array
     uint16_t    length;   // Number of steps in the array
     uint8_t     mode;     // SHOW_LOOP or SHOW_SINGLE
+    uint8_t     flags;    // Bitfield: see SHOW_FLAG_* above
 };
 
 // Read one Step from PROGMEM into a regular struct.
@@ -47,5 +51,6 @@ inline ShowDef read_show_def(const ShowDef* ptr) {
     sd.steps  = (const Step*)pgm_read_word(&ptr->steps);
     sd.length = pgm_read_word(&ptr->length);
     sd.mode   = pgm_read_byte(&ptr->mode);
+    sd.flags  = pgm_read_byte(&ptr->flags);
     return sd;
 }