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>

converter/shows/003_blue_sparkle.txt

@@ -0,0 +1,10 @@
+// Blue breath with sparkle overlay
+//
+// flags: sparkle
+// mode: loop
+
+#050018,    0   // snap to near-black blue
+#2020FF, 2500   // breathe in — slow rise to bright blue
+#2020FF,  400   // hold at peak
+#050018, 2500   // breathe out — slow fall to near-black
+#050018,  800   // pause before next breath