fix(onboarding): step counter ignores skipped steps; transparent + tight BB poses

Three bugs in the tour shipped in the previous commit:

    - The step counter displayed raw index over total, so when add-printer
      auto-skipped (printer already configured), the first visible step
      rendered as "2 / 25". Counter now shows visible position over visible
      total — that user sees "1 / 24". Same trick handles every other
      skipIf-gated step (makerworld permission, sso/users when auth off).

    - The BB mascot crops were lossy webp with no alpha, so the off-white
      sheet background showed as a hard rectangle against the dark-theme
      tour card. Re-sliced from the source character sheet as lossless
      webp RGBA with a soft alpha ramp on the background, so the mascot
      composites cleanly.

    - The same crops included the caption text below each pose ("Almost
      there!" etc.), visible as a sliver under the character. Tightened
      the Y range to exclude the caption row.

    scripts/slice_bb_mascot.py captures the pose coordinates and the
    keyout ramp so a future character-sheet re-export is reproducible
    rather than nudged by eye.

scripts/slice_bb_mascot.py

@@ -0,0 +1,70 @@
+"""Re-slice BB mascot poses from the character sheet.
+
+Produces the per-pose webp files consumed by MascotIcon (the onboarding tour).
+
+Source:  screenshots/onboarding/bb_bambuddy.webp (RGB, no alpha, opaque bg)
+Output:  frontend/public/img/bb_{hero,started,walk,almost,allset,help}.webp
+
+Two things matter and must not regress:
+  - the crop excludes the caption text under each pose, so the tour modal
+    never shows a sliver of "Almost there!" under the character;
+  - the background is keyed out to alpha so the mascot composites cleanly
+    on the dark-theme tour card.
+
+Pose coordinates are pixel offsets in the source sheet, derived once by
+column/row density analysis. If the character sheet is re-exported with
+different dimensions, re-derive them rather than nudging by eye.
+"""
+
+from pathlib import Path
+
+import numpy as np
+from PIL import Image
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+SRC = REPO_ROOT / "screenshots/bb images/bb_bambuddy.webp"
+OUT_DIR = REPO_ROOT / "frontend/public/img"
+
+POSE_Y = (746, 924)
+POSES = {
+    "started": (35, 206),
+    "walk": (251, 423),
+    "almost": (455, 631),
+    "allset": (657, 851),
+    "help": (861, 1079),
+}
+HERO_BOX = (50, 71, 620, 650)
+
+# Background ramp: pixels with min-channel >= BG_FULL go fully transparent,
+# pixels with min-channel <= INK stay fully opaque, in between alpha ramps
+# linearly so anti-aliased outlines keep their feathering.
+BG_FULL = 228
+INK = 200
+
+
+def keyout_to_alpha(crop: Image.Image) -> Image.Image:
+    arr = np.array(crop.convert("RGB"))
+    min_ch = arr.min(axis=2).astype(np.int32)
+    alpha = np.clip((BG_FULL - min_ch) * 255 // (BG_FULL - INK), 0, 255).astype(np.uint8)
+    return Image.fromarray(np.dstack([arr, alpha]), mode="RGBA")
+
+
+def save_webp_lossless(im: Image.Image, path: Path) -> None:
+    im.save(path, "WEBP", lossless=True, quality=100, method=6)
+
+
+def main() -> None:
+    src = Image.open(SRC)
+    for name, (x0, x1) in POSES.items():
+        crop = src.crop((x0, POSE_Y[0], x1, POSE_Y[1]))
+        out_path = OUT_DIR / f"bb_{name}.webp"
+        save_webp_lossless(keyout_to_alpha(crop), out_path)
+        print(f"  {out_path.name}  {crop.size}")
+
+    hero_crop = src.crop(HERO_BOX)
+    save_webp_lossless(keyout_to_alpha(hero_crop), OUT_DIR / "bb_hero.webp")
+    print(f"  bb_hero.webp  {hero_crop.size}")
+
+
+if __name__ == "__main__":
+    main()