Parallelize repository cloning during dev environment setup

[Copilot]

Sequential git clone calls during composer install/composer update made initial dev environment setup unnecessarily slow. The refresh step already used xargs for parallelism; cloning did not.

Changes

• New .maintenance/clone-all-repositories.sh: Bash script that orchestrates the full clone + refresh flow. Detects CPU cores via nproc (Linux) or sysctl -n hw.logicalcpu (macOS), defaulting to 4 if neither is available. Fetches the repository list from the GitHub API using curl, parses JSON with jq, filters the skip list, applies the destination map, then clones missing repos and refreshes all repos in parallel using xargs -P$CORES.
• New .maintenance/clone-repository.sh: Bash helper that clones a single repository, accepting <destination> and <clone_url> as arguments.
• Removed .maintenance/clone-all-repositories.php and .maintenance/clone-repository.php.
• Updated composer.json: pre-install-cmd and pre-update-cmd now call bash .maintenance/clone-all-repositories.sh.

# Detect CPU cores, default to 4
if command -v nproc &>/dev/null; then
    CORES=$(nproc)
elif command -v sysctl &>/dev/null; then
    CORES=$(sysctl -n hw.logicalcpu 2>/dev/null || echo 4)
else
    CORES=4
fi

# Clone and refresh in parallel, bounded by core count
printf '%s\n' "${CLONE_LIST[@]}" | xargs -n2 -P"${CORES}" bash clone-repository.sh
printf '%s\n' "${UPDATE_FOLDERS[@]}" | xargs -n1 -P"${CORES}" -I% php refresh-repository.php %