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/006_party.txt

@@ -0,0 +1,22 @@
+// Party mode — rapid rainbow color flashes
+// Plays once then auto-advances to the next show.
+//
+// mode: single
+
+#FF0000,    0   // snap to red
+#FF0000,  150   // hold red
+#FF8800,    0   // snap to orange
+#FF8800,  150   // hold orange
+#FFFF00,    0   // snap to yellow
+#FFFF00,  150   // hold yellow
+#00FF00,    0   // snap to green
+#00FF00,  150   // hold green
+#00FFFF,    0   // snap to cyan
+#00FFFF,  150   // hold cyan
+#0000FF,    0   // snap to blue
+#0000FF,  150   // hold blue
+#FF00FF,    0   // snap to magenta
+#FF00FF,  150   // hold magenta
+#FFFFFF,    0   // snap to white
+#FFFFFF,  150   // hold white
+#000000,  500   // fade to off — brief pause before advancing