Lift time range state into a shared React context so the selected
range persists across page navigation and browser refreshes
(localStorage). Add a "Custom" option with a popover date picker
that lets users specify arbitrary start/end dates. All preset end
times now use endOf("day") (23:59:59) instead of the current moment.
Full-screen landing page with glassmorphism cards linking to monitoring
(8018), docs (8017), and analytics (8019). Sidebar is conditionally
hidden on the portal route. Supports dark/light themes and i18n.
