perf(clean): speed up scan phase across all modules

- Parallelize project cache indicator checks and root scans in caches.sh
  (sequential find per $HOME/* dir → throttled background jobs)
- Pre-compute project name cache before purge display loop, eliminating
  O(N²) filesystem traversals in get_artifact_display_name
- Replace basename/dirname subshells with parameter expansion in
  get_project_name/get_project_path hot loops; depth counter via
  bash string arithmetic instead of echo|tr|wc|tr pipeline
- Eliminate mktemp/awk/rm per call in app_support_item_size_bytes,
  use command substitution to capture du output directly
- Defer tr lowercase in clean_application_support_logs to only when
  first 3 protection checks fail; replace basename with ${var##*/}
- Optimize trash item counting: find -print0|tr -dc '\0'|wc -c
  avoids per-file fork from -exec printf
- Add -maxdepth 5 to /private/var/folders find (X dir is always at
  depth 3, code_sign_clone at depth 5 max; verified on real machine)

lib/clean/system.sh

@@ -155,7 +155,7 @@ clean_deep_system() {
         if safe_sudo_remove "$cache_dir"; then
             code_sign_cleaned=$((code_sign_cleaned + 1))
         fi
-    done < <(run_with_timeout 5 command find /private/var/folders -type d -name "*.code_sign_clone" -path "*/X/*" -print0 2> /dev/null || true)
+    done < <(run_with_timeout 5 command find /private/var/folders -maxdepth 5 -type d -name "*.code_sign_clone" -path "*/X/*" -print0 2> /dev/null || true)
     stop_section_spinner
     [[ $code_sign_cleaned -gt 0 ]] && log_success "Browser code signature caches, $code_sign_cleaned items"