fix(installer): install gettext headers on Alpine (#222)

local/uvr-install.sh

@@ -16,8 +16,8 @@
 # precisely because such a target may be shared (`/mnt/cache/R-pkgs` holds
 # bincraft and its dependencies alongside whatever this script installs).
 #
-# System dependencies come from uvr's vendored r-system-requirements rules, so
-# `pak::sysreqs_db_update()` and `PKG_SYSREQS_PLATFORM` are no longer needed.
+# System dependencies come from uvr's vendored r-system-requirements rules,
+# with explicit prerequisites below for gaps in Alpine support.
 #
 # Environment:
 #   UVR_R_BIN        R interpreter to install for; set by install-bincraft.R so
@@ -117,4 +117,11 @@ if command -v apt-get >/dev/null 2>&1; then
   apt-get update -qq || echo "warning: apt-get update failed; continuing" >&2
 fi
 
+# Alpine's build images lack libintl.h, which data.table needs when R enables
+# NLS. uvr does not resolve this prerequisite on Alpine, so install it before
+# compiling bincraft's dependencies (including when the library cache is cold).
+if command -v apk >/dev/null 2>&1; then
+  apk add --no-cache gettext-dev
+fi
+
 "$uvr_bin" sync --library "$target_lib" --install-system-deps