feat: harden user file handling and gate LaunchServices rebuild (#159)

- add ensure_user_dir/ensure_user_file helpers in lib/core/base.sh, including
  sudo-aware ownership correction under the invoking user’s home
- use the helpers across clean/optimize/purge/uninstall/whitelist to create
  cache and export files safely (no naked mkdir/touch), including log files and
  dry-run exports
- ensure purge stats/count files and update message caches are pre-created with
  safe permissions
- add Darwin version helpers and skip LaunchServices/dyld rebuild on macOS 15+,
  keeping the existing corruption protection for earlier versions
- guard brew cache timestamp writes and TCC permission flags with safe file
  creation to avoid root-owned artifacts

bin/purge.sh

@@ -47,7 +47,9 @@ start_purge() {
 
     # Initialize stats file in user cache directory
     local stats_dir="${XDG_CACHE_HOME:-$HOME/.cache}/mole"
-    mkdir -p "$stats_dir"
+    ensure_user_dir "$stats_dir"
+    ensure_user_file "$stats_dir/purge_stats"
+    ensure_user_file "$stats_dir/purge_count"
     echo "0" > "$stats_dir/purge_stats"
     echo "0" > "$stats_dir/purge_count"
 }