build: replace ad-hoc run with a full make workflow + helper scripts

The old Makefile was a single 'run' target (hugo server + pagefind --serve).
Replace it with documented targets:

  build         hugo --gc -> public/
  index         build + pagefind --site public -> public/pagefind/
  serve / run   index + pagefind's own server on 127.0.0.1:1414 (local)
  serve-lan     static-serve public/ on 0.0.0.0:8090 for other machines
  link-check    offline internal-link scan (lychee --scheme file) -> JSON
  link-fix      comment out confirmed-dead internal links, then rebuild
  external-check network scan of external links (report-only)
  clean / all

Add scripts/:
  serve_lan.py            stdlib static server rooted at public/ (prints LAN IP)
  fix_dead_links.py       idempotent internal dead-link comment-out
  check_external_links.py external link report (drives the daily cron job)

.gitignore: add linkcheck/, resources/_gen/ (regenerable Hugo asset cache),
__pycache__/, and .hermes/.

.gitignore

@@ -1 +1,5 @@
 **/public/
+linkcheck/
+resources/_gen/
+__pycache__/
+.hermes/