Refactor: fix socket leak, deduplicate stat/path logic, simplify config

- get_local_ip: use context manager to prevent socket leak
- _route_files: single stat() per file instead of two
- _safe_path helper: DRY path resolution for download/delete
- load_config: loop over vars(args) instead of 6 repetitive blocks
- Remove stale comment from index.html

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

static/index.html

@@ -259,8 +259,6 @@ $('lang-sw').addEventListener('click', e => {
   if (e.target.dataset.l) setLang(e.target.dataset.l);
 });
 
-/* File type is determined server-side via /files API ("text" | "image" | "other") */
-
 /* ── Helpers ── */
 
 let toastTimer;