feat: add application versioning support to backend and UI

- Introduce APP_VERSION build argument and environment variable in Dockerfile.
- Load AppVersion from environment variables in the configuration loader.
- Pass the application version to the HTML renderer and expose it to templates via PageData.
- Update tests to verify the version is correctly rendered in the footer.

scripts/run/dev.sh

@@ -14,6 +14,11 @@ set -a
 source "${ENV_FILE}"
 set +a
 
+if [[ -z "${APP_VERSION:-}" ]]; then
+  APP_VERSION="$(git -C "${ROOT_DIR}" describe --tags --abbrev=0 2>/dev/null || printf 'dev')"
+  export APP_VERSION
+fi
+
 if [[ "${WARPBOX_DATA_DIR:-}" != /* ]]; then
   export WARPBOX_DATA_DIR="${ROOT_DIR}/${WARPBOX_DATA_DIR:-data}"
 fi