Add System Admin area and redesign Competitions page

Move the Users table and add a new rule-text editor into a dedicated
admin.html/admin.js page with its own collapsible sidebar (Users,
Rules categories), reachable only for system admins via a button next
to the brand. The Competitions page no longer renders admin-only
controls inline.

Competitions page: cards are now fully clickable to open the
competition (drop the separate "Open" button), the admin-only delete
action moves into a "..." menu (new generic openInlineMenu/
openAnchoredPopover helpers in common.js), and add an open/closed
filter.

Topbar: language switch and logout move out of the topbar into a
small popup under the profile button, which itself opens the full
settings modal for username/display name/language/password.

web/api.js

@@ -81,6 +81,9 @@ const API = {
 
   listRules: (lang) => api("GET", `/api/rules${lang ? "?lang=" + encodeURIComponent(lang) : ""}`),
   listRuleLanguages: () => api("GET", "/api/rules/languages"),
+  listRuleNumbers: () => api("GET", "/api/rules/numbers"),
+  updateRule: (lang, number, b) => api("PUT", `/api/rules/${encodeURIComponent(lang)}/${encodeURIComponent(number)}`, b),
+  reloadRules: () => api("POST", "/api/rules/reload"),
 };
 
 function openCompetitionWS(id, handlers) {