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/find-R-api-packages.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+# Directory to clone repos into
+WORKDIR="cran_repos"
+mkdir -p "$WORKDIR"
+cd "$WORKDIR"
+
+# GitHub API paginates results, so we loop through pages
+PAGE=1
+PER_PAGE=100
+MATCHES=()
+
+while :; do
+    # Fetch a page of repos
+    REPOS=$(curl -s "https://api.github.com/orgs/cran/repos?per_page=$PER_PAGE&page=$PAGE" | jq -r '.[].clone_url')
+    [ -z "$REPOS" ] && break
+
+    for REPO_URL in $REPOS; do
+        REPO_NAME=$(basename "$REPO_URL" .git)
+        # Skip if already cloned
+        [ -d "$REPO_NAME" ] && continue
+        git clone --depth 1 "$REPO_URL" "$REPO_NAME" >/dev/null 2>&1
+        if [ -d "$REPO_NAME/src" ]; then
+            # Search for Rinternals.h in src/
+            if grep -r -q 'R_VERSION < R_Version(' "$REPO_NAME/src"; then
+                echo "$REPO_NAME"
+            fi
+        fi
+        # Clean up to save space
+        rm -rf "$REPO_NAME"
+    done
+
+    PAGE=$((PAGE + 1))
+done