Add DNS accounts, Let's Encrypt, password change, reboot, HTTP redirect

- router.dnsProviders: named accounts at DNS providers, used by dynamic
  DNS and certificates (ddclient and lego provider lists in
  pkgs/router-webui/providers.json). Schema 2 migrates router.ddns.
- router.acme: a Let's Encrypt certificate for the web UI via
  security.acme (DNS-01, resolver 1.1.1.1), served and reloaded by the
  web UI; Certificate page.
- Web UI: password change (web UI and root), reboot button, HTTP to HTTPS
  redirect (router.webui.httpPort), grouped menu.
- Latest kernel (linuxPackages_latest); 7.3 and 7.3.0 are the same kernel
  for the reboot hint.
- SPECS.md: wanted later (REST API, GraphQL, MCP).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

pkgs/router-webui/static/menu.js

@@ -0,0 +1,13 @@
+// Menus close on a click elsewhere; forms with data-confirm ask first.
+// Close an open menu when the click is somewhere else.
+document.addEventListener("click", function (e) {
+  document.querySelectorAll("nav details[open]").forEach(function (d) {
+    if (!d.contains(e.target)) d.removeAttribute("open");
+  });
+});
+
+// Ask before a form marked data-confirm is sent.
+document.addEventListener("submit", function (e) {
+  var q = e.target.getAttribute("data-confirm");
+  if (q && !confirm(q)) e.preventDefault();
+});