feat: harden pipeline UX — preprocess, rembg alpha, remix/lightbox

Downscale to 2000px JPEG before rembg, random blend opacity, timeout
retries, per-variant remix prefill, lightbox, and longer SFTP idle.

Co-authored-by: Cursor <cursoragent@cursor.com>

compare-bg/run.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# Run rembg/withoutbg comparison in Python 3.11 (host is 3.14-only).
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")" && pwd)"
+IMG="livef12-bg-compare:py311"
+LOG="$ROOT/compare.log"
+
+docker build -t "$IMG" - <<'EOF'
+FROM python:3.11-slim-bookworm
+RUN apt-get update && apt-get install -y --no-install-recommends libgl1 libglib2.0-0 \
+    && rm -rf /var/lib/apt/lists/*
+RUN pip install --no-cache-dir 'rembg>=2.0.59,<2.1' 'pillow>=10.4,<11' \
+    'onnxruntime>=1.19,<1.20' withoutbg
+WORKDIR /work
+EOF
+
+echo "Starting comparison; log: $LOG"
+docker run --rm \
+  --name livef12-bg-compare \
+  -e TQDM_DISABLE=1 \
+  -e COMPARE_INPUT=/data/inputs \
+  -e COMPARE_OUTPUT=/data/outputs \
+  -e HOME=/cache \
+  -v "$ROOT/inputs:/data/inputs:ro" \
+  -v "$ROOT/outputs:/data/outputs" \
+  -v "$ROOT/run_compare.py:/work/run_compare.py:ro" \
+  -v "$ROOT/model-cache:/cache" \
+  "$IMG" python -u /work/run_compare.py 2>&1 | tee "$LOG"