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>

tools/gen_skin_template.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""
+gen_skin_template.py — Generate a skin template PNG for sdlamp2.
+
+Creates a 642x420 PNG showing the sprite grid layout with labeled gutters.
+Each 200x200 cell is blank white (ready to draw on). The 20px gutters between
+cells are gray with small text labels identifying adjacent cells.
+
+Grid layout:
+  Col 0 (0-199)    Col 1 (220-419)   Col 2 (440-639)
+  Row 0: REWIND     PLAY              FF
+         ----gutter y=200-219 with labels----
+  Row 1: STOP       PREV              NEXT
+
+Two extra pixels on the right (640-641) are gutter fill to reach 642px width,
+matching the spritesheet dimensions.
+
+Usage: python3 tools/gen_skin_template.py [output.png]
+
+Requires Pillow.
+"""
+import sys
+
+from PIL import Image, ImageDraw, ImageFont
+
+CELL = 200
+GAP = 20
+COLS = 3
+ROWS = 2
+WIDTH = COLS * CELL + (COLS - 1) * GAP + 2   # 642
+HEIGHT = ROWS * CELL + (ROWS - 1) * GAP       # 420
+
+CELL_COLOR = (255, 255, 255)
+GUTTER_COLOR = (180, 180, 180)
+TEXT_COLOR = (80, 80, 80)
+
+LABELS = [
+    ["REWIND", "PLAY", "FF"],
+    ["STOP", "PREV", "NEXT"],
+]
+
+
+def cell_x(col):
+    return col * (CELL + GAP)
+
+
+def cell_y(row):
+    return row * (CELL + GAP)
+
+
+def main():
+    output_path = sys.argv[1] if len(sys.argv) > 1 else "skin_template.png"
+
+    img = Image.new("RGB", (WIDTH, HEIGHT), GUTTER_COLOR)
+    draw = ImageDraw.Draw(img)
+
+    # Try to load a small font for labels
+    try:
+        font = ImageFont.truetype("/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf", 11)
+    except OSError:
+        try:
+            font = ImageFont.truetype("/System/Library/Fonts/Helvetica.ttc", 11)
+        except OSError:
+            font = ImageFont.load_default()
+
+    # Draw white cells
+    for row in range(ROWS):
+        for col in range(COLS):
+            x = cell_x(col)
+            y = cell_y(row)
+            draw.rectangle([x, y, x + CELL - 1, y + CELL - 1], fill=CELL_COLOR)
+
+    # Label the horizontal gutter (y = 200..219)
+    gutter_y = CELL  # 200
+    for col in range(COLS):
+        cx = cell_x(col) + CELL // 2
+
+        # Row 0 label above center of gutter
+        label_0 = LABELS[0][col]
+        bbox = draw.textbbox((0, 0), label_0, font=font)
+        tw = bbox[2] - bbox[0]
+        draw.text((cx - tw // 2, gutter_y + 1), label_0, fill=TEXT_COLOR, font=font)
+
+        # Row 1 label below center of gutter
+        label_1 = LABELS[1][col]
+        bbox = draw.textbbox((0, 0), label_1, font=font)
+        tw = bbox[2] - bbox[0]
+        th = bbox[3] - bbox[1]
+        draw.text((cx - tw // 2, gutter_y + GAP - th - 2), label_1, fill=TEXT_COLOR, font=font)
+
+    img.save(output_path)
+    print(f"Skin template saved to {output_path} ({WIDTH}x{HEIGHT})")
+
+
+if __name__ == "__main__":
+    main()