Add script to predownload offline build dependencies

scripts/predownload-offline-deps.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+cache_dir="target/sqlpage_artefacts"
+mkdir -p "$cache_dir"
+
+echo "[1/3] Prefetching Cargo dependencies"
+cargo fetch --locked
+
+echo "[2/3] Prefetching npm dependencies"
+npm ci --ignore-scripts --no-audit
+if [ -f tests/end-to-end/package-lock.json ]; then
+    (
+        cd tests/end-to-end
+        npm ci --ignore-scripts --no-audit
+    )
+fi
+
+echo "[3/3] Prefetching raw HTTP assets used by build.rs"
+mapfile -t urls < <(
+    {
+        rg -o --no-filename 'https://[[:alnum:]][[:alnum:].-]*/[^" )]+' build.rs
+        rg -o --no-filename '^/\* !include https://[^ ]+' sqlpage/*.css sqlpage/*.js sqlpage/*.svg \
+            | sed 's#^/\* !include ##'
+    } | sort -u
+)
+
+for url in "${urls[@]}"; do
+    file_name=$(printf '%s' "$url" | sed -E 's/[^[:alnum:].-]/_/g')
+    cache_file="$cache_dir/$file_name"
+
+    if [ -s "$cache_file" ]; then
+        echo "  - Cached: $url"
+        continue
+    fi
+
+    echo "  - Downloading: $url"
+    curl -fsSL "$url" -o "$cache_file"
+done
+
+echo "Done. Offline caches are ready."