Add bootstrap and cached repository scripts

bootstrap.sh clones from a local mirror and extracts framework
files into the working directory. update-cached-repository.sh
maintains the mirror under ~/.cache/diachron/v1/repositories/.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

update-cached-repository.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+set -eu
+set -o pipefail
+IFS=$'\n\t'
+
+trap 's=$?; echo >&2 "$0: Error on line "$LINENO": $BASH_COMMAND"; exit $s' ERR
+
+upstream=https://gitea.philologue.net/philologue/diachron
+cache_dir="$HOME/.cache/diachron/v1/repositories"
+cached_repo="$cache_dir/diachron.git"
+
+mkdir -p "$cache_dir"
+
+if [ -d "$cached_repo" ]; then
+    echo "Updating cached repository..."
+    git -C "$cached_repo" fetch --prune origin
+else
+    echo "Creating cached repository..."
+    git clone --mirror "$upstream" "$cached_repo"
+fi
+