fix(ci): reclaim space for semantic backup smoke

scripts/prepare-linux-docker-runner.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# The local distribution gate pulls the 7 GB Ollama image, downloads the default embedding
+# model, builds the application images, and then archives every durable volume. GitHub's hosted
+# Linux image also ships toolchains this job never uses. Remove only those known, runner-owned
+# installations so the backup is tested with the production semantic stack instead of a stub.
+[[ "$(uname -s)" == Linux ]] || {
+  printf 'Linux is required for hosted-runner disk preparation.\n' >&2
+  exit 1
+}
+
+readonly unused_toolchains=(
+  /usr/local/lib/android
+  /usr/share/dotnet
+  /opt/ghc
+  /usr/local/.ghcup
+)
+
+for path in "${unused_toolchains[@]}"; do
+  [[ -e "$path" || -L "$path" ]] || continue
+  sudo rm -rf -- "$path"
+done
+
+sudo apt-get clean
+docker system prune --all --force
+df -h /
+docker system df