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.
