chore(local): add S3 migration and CRAN-source helper scripts

- migrate-s3-hetzner-to-backblaze.sh: rclone-based bucket migration helper.
- find-R-api-packages.sh: scan CRAN package sources for a C-API usage pattern.
- query-pkgs-without-old-versions.R, test-package-loading.R: ad-hoc helpers.

local/migrate-s3-hetzner-to-backblaze.sh

@@ -0,0 +1,90 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Migrate S3 buckets from Hetzner Object Storage to Backblaze B2 via rclone.
+#
+# Prerequisites:
+#   1. Install rclone: https://rclone.org/install/
+#   2. Configure two rclone remotes:
+#        rclone config create hetzner s3 \
+#          provider=Other \
+#          env_auth=false \
+#          access_key_id=YOUR_HETZNER_KEY \
+#          secret_access_key=YOUR_HETZNER_SECRET \
+#          endpoint=fsn1.your-objectstorage.com   # adjust region
+#
+#        rclone config create backblaze s3 \
+#          provider=Other \
+#          env_auth=false \
+#          access_key_id=YOUR_B2_KEY \
+#          secret_access_key=YOUR_B2_APP_KEY \
+#          endpoint=s3.us-west-004.backblazeb2.com  # adjust region
+#
+# Usage:
+#   ./migrate-s3-hetzner-to-backblaze.sh <src:dst> [src:dst] ...
+#   ./migrate-s3-hetzner-to-backblaze.sh hetzner-bucket:backblaze-bucket
+
+HETZNER_REMOTE="${HETZNER_REMOTE:-hetzner}"
+BACKBLAZE_REMOTE="${BACKBLAZE_REMOTE:-backblaze}"
+RCLONE_FLAGS="${RCLONE_FLAGS:---transfers=64 --checkers=64 --fast-list}"
+
+if [[ $# -eq 0 ]]; then
+  echo "Usage: $0 <src-bucket:dst-bucket> [src-bucket:dst-bucket...]"
+  echo ""
+  echo "  Each argument is a source:destination bucket pair separated by a colon."
+  echo ""
+  echo "Environment variables:"
+  echo "  HETZNER_REMOTE   rclone remote name for Hetzner (default: hetzner)"
+  echo "  BACKBLAZE_REMOTE rclone remote name for Backblaze (default: backblaze)"
+  echo "  RCLONE_FLAGS     extra rclone flags (default: --transfers=16 --checkers=16 --fast-list)"
+  echo "  DRY_RUN=1        show what would be copied without copying"
+  exit 1
+fi
+
+for cmd in rclone; do
+  if ! command -v "$cmd" &>/dev/null; then
+    echo "Error: $cmd is not installed." >&2
+    exit 1
+  fi
+done
+
+# Verify remotes exist
+for remote in "$HETZNER_REMOTE" "$BACKBLAZE_REMOTE"; do
+  if ! rclone listremotes | grep -q "^${remote}:$"; then
+    echo "Error: rclone remote '${remote}' not found. Run 'rclone config' to set it up." >&2
+    exit 1
+  fi
+done
+
+DRY_RUN_FLAG=""
+if [[ "${DRY_RUN:-0}" == "1" ]]; then
+  DRY_RUN_FLAG="--dry-run"
+  echo "=== DRY RUN MODE ==="
+fi
+
+for pair in "$@"; do
+  if [[ "$pair" != *:* ]]; then
+    echo "Error: '$pair' is not a valid src:dst pair. Use format 'hetzner-bucket:backblaze-bucket'." >&2
+    exit 1
+  fi
+
+  src_bucket="${pair%%:*}"
+  dst_bucket="${pair#*:}"
+  src="${HETZNER_REMOTE}:${src_bucket}"
+  dst="${BACKBLAZE_REMOTE}:${dst_bucket}"
+
+  echo ""
+  echo "--- Migrating: ${src} -> ${dst} ---"
+
+  # shellcheck disable=SC2086
+  rclone sync \
+    ${RCLONE_FLAGS} \
+    ${DRY_RUN_FLAG} \
+    --progress \
+    "$src" "$dst"
+
+  echo "--- Done: ${src_bucket} -> ${dst_bucket} ---"
+done
+
+echo ""
+echo "Migration complete."