feat(updates): seamless release flow — push-notify, VERSION copy, robust mirror

- self-updater: per-instance notify secret (auto-generated), notifyAndApply()
  triggers an immediate check+apply for the publishing host
- routes: POST /api/system/update-notify (X-DashCaddy-Notify-Secret gated,
  added to public-routes allowlist so TOTP doesn't block machine-to-machine)
- dashcaddy-update.sh: include VERSION in backup/deploy/rollback copy lists;
  belt-and-suspenders write trigger.json commit to VERSION post-deploy.
  Fixes drift where /app/VERSION stayed at the old commit after self-update.
- release.sh: mirror failures are non-fatal+loud; HTTP-verify get2 after
  rsync; auto-notify co-located instance via /opt/dashcaddy/updates/notify-secret
  (or honour DASHCADDY_NOTIFY_TARGETS for multi-instance setups).

status/index.html

@@ -8,7 +8,7 @@
   <meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate" />
   <meta http-equiv="Pragma" content="no-cache" />
   <meta http-equiv="Expires" content="0" />
-  <meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' 'sha256-Nv8xzCSztfdYOL663VgPKWQn6v0lnM0ACWxkxpFfcfY='; style-src 'self' 'unsafe-inline'; img-src 'self' https://cdn.jsdelivr.net data:; connect-src 'self' https://api.open-meteo.com https://geocoding-api.open-meteo.com; font-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'">
+  <meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' 'sha256-kwm9nLWm/jfIuT8y4i62Xq6mDqe4mRlMZn1tDg+5Zek='; style-src 'self' 'unsafe-inline'; img-src 'self' https://cdn.jsdelivr.net data:; connect-src 'self' https://api.open-meteo.com https://geocoding-api.open-meteo.com; font-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'">
 
   <link rel="icon" href="/assets/dashcaddy-favicon.ico" sizes="any">
   <link rel="icon" type="image/png" sizes="192x192" href="/assets/icon-192.png">