fix: install.sh loop abort, ACME poll sudo gate, /static/ sub-paths

- install.sh: the traversal-chmod loop assigned _d but looped over the
  never-set $d; under set -u every fresh install aborted with
  "d: unbound variable" at that line. Loop over $_d.
- acme collector: the self-heal normalize (sudo chmod g+rwX) now runs
  only when a no-sudo group-read-bit probe detects a lost bit — acme.sh
  re-hardens the tree 600 on every run, so the steady-state poll makes
  no sudo call. The group bit (not daemon readability) is what the
  two-user model keeps for the WebUI user.
- lib.acme: new get_acme_home() accessor (ACME_HOME env, default
  data/acme), reused by _run_acme; _summarize_acme_output preserves a
  "Permission denied" line even when it is not among the final two, so
  the collector's actionable-error matcher keeps firing.
- nginx template: emit location /static/ for any is_management path
  (not only '/'); the SPA references /static/... at the domain root
  regardless of the management backend path.
- tests: probe, summarizer, and nginx-subpath cases in
  test_state.py, test_acme.py, test_nginx.py.

system/nginx/server_block.conf

@@ -53,7 +53,7 @@ server {
 {% endif %}
 
 {% for ppath, pcfg in paths.items() %}
-{% if pcfg.is_management and ppath == '/' %}
+{% if pcfg.is_management %}
     # SPA static assets — served from disk, no Flask round-trip.
     # no-cache: browsers revalidate every load; unchanged files are 304s.
     location /static/ {