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/optimize.sh

@@ -200,7 +200,7 @@ cleanup_path() {
 ensure_directory() {
     local raw_path="$1"
     local expanded_path="${raw_path/#\~/$HOME}"
-    mkdir -p "$expanded_path" > /dev/null 2>&1 || true
+    ensure_user_dir "$expanded_path"
 }
 
 count_local_snapshots() {