Skin template system, separate prev sprite, reorganize device scripts

Add tools/gen_skin_template.py to generate a labeled 642x420 PNG template
for creating custom spritesheets. Move rg35xx device scripts from tools/
to device/rg35xx/. Point prev_sprite at its own cell (bottom-center) so
Prev and Next can have distinct icons.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

device/rg35xx/rg35xx-wrapper.sh

@@ -0,0 +1,69 @@
+#!/bin/sh
+#
+# RG35XX Plus wrapper for sdlamp2
+#
+# Launched by dmenu_ln instead of sdlamp2 directly. Handles device-specific
+# concerns that don't belong in the player binary:
+#   1. Screen idle timeout, power button screen toggle, and long-press shutdown
+#   2. Display the stock firmware's shutdown screen (goodbye.png → /dev/fb0)
+#   3. Launch sdlamp2 as the main process
+#
+# Install: copy to /mnt/vendor/bin/rg35xx-wrapper.sh
+# Config:  set CMD in dmenu_ln to point here instead of sdlamp2 directly
+
+SDLAMP2="/mnt/vendor/bin/sdlamp2"
+AUDIO_DIR="/mnt/sdcard/Music"
+SCREEN_MONITOR="/mnt/vendor/bin/rg35xx-screen-monitor.py"
+
+# --- WiFi hotspot ---
+# Deprioritized: connecting the device as a WiFi client to a shared network
+# works fine even when sdlamp2 replaces the stock menu. Hotspot/AP mode isn't
+# needed — SSH access works over the shared network.
+
+# --- Launch sdlamp2 ---
+"$SDLAMP2" "$AUDIO_DIR" &
+SDLAMP2_PID=$!
+
+# --- Screen monitor (idle timeout + power button toggle + long-press shutdown) ---
+# Must launch after sdlamp2 so PID is available. Reads /dev/input/event0
+# directly for power button events — no evtest dependency.
+python3 "$SCREEN_MONITOR" "$SDLAMP2_PID" &
+SCREEN_MONITOR_PID=$!
+
+# Wait for sdlamp2 to finish (signal or normal exit).
+wait "$SDLAMP2_PID"
+SDLAMP2_EXIT=$?
+
+# --- Cleanup ---
+# Kill the screen monitor (SIGTERM restores brightness).
+kill "$SCREEN_MONITOR_PID" 2>/dev/null
+wait "$SCREEN_MONITOR_PID" 2>/dev/null
+
+# If this was a shutdown, call poweroff and block so the loadapp.sh restart
+# loop doesn't relaunch dmenu_ln (which would take over the framebuffer and
+# overwrite sdlamp2's shutdown screen).
+if [ -f /tmp/.sdlamp2_shutdown ]; then
+  rm -f /tmp/.sdlamp2_shutdown
+  # Restore backlight brightness before writing the shutdown screen.
+  # The screen monitor's SIGTERM handler tries to restore brightness, but
+  # the Allwinner /dev/disp driver resets it to 0 when the fd is closed.
+  # Re-set it here so goodbye.png is actually visible.
+  # Then display the stock firmware's shutdown screen via framebuffer.
+  # goodbye.png is 640x480 RGB — exactly matches the display.
+  # /dev/fb0 is 32bpp BGRA, so we swap R/B channels and write raw pixels.
+  python3 -c "
+import struct, fcntl
+disp = open('/dev/disp', 'wb')
+fcntl.ioctl(disp, 0x102, struct.pack('@4L', 0, 50, 0, 0))
+disp.close()
+from PIL import Image
+img = Image.open('/mnt/vendor/res1/shutdown/goodbye.png').convert('RGBA')
+r, g, b, a = img.split()
+with open('/dev/fb0', 'wb') as f:
+    f.write(Image.merge('RGBA', (b, g, r, a)).tobytes())
+" 2>/dev/null
+  poweroff
+  sleep 30
+fi
+
+exit "$SDLAMP2_EXIT"