build(space): remove packages.txt; install Tectonic via postBuild using install_tectonic.sh

packages.txt

@@ -1 +0,0 @@
-tectonic

postBuild

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "[postBuild] Ensuring wget present and installing Tectonic"
+if ! command -v wget >/dev/null 2>&1; then
+  apt-get update
+  apt-get install -y wget
+fi
+
+bash install_tectonic.sh || echo "[postBuild] Tectonic install script returned non-zero; continuing."
+
+echo "[postBuild] Done"