ui: fix admin/docs theme flash + persist sidebar open/closed state

Theme flash (admin pages, docs, stats, progress — anywhere SSR'd):
the JWT middlewares built the context user WITHOUT the Theme column,
so every page rendering theme-{user.Theme} from c.Get("user") painted
an empty class (:root tokyo-night default) and only settled on the real
theme after initializeTheme -> loadUserTheme round-tripped the server.
Both middlewares now carry liveUser.Theme into the context user;
verified live: /admin /stats /progress /docs /docs-deep /dashboard
/collections all SSR theme-hackerman.

Defense in depth for the same bug: loadTheme() no longer re-applies
localStorage over a server-rendered body theme (applyTheme records even
the default, so any signed-out visit baked tokyo-night into localStorage
and every signed-in page flipped to it post-paint). Public auth/landing
bodies dropped their hardcoded theme classes so ThemeFlashGuard's
pre-paint html class actually governs them; docs theme <select> now
syncs from the body class and re-syncs after the profile fetch.

Sidebar state (the unpleasant part): the app sidebar's openPanel was
reinitialized from the pathname on every load; it now restores from
localStorage ('sidebar-open-panel') with the pathname default as
fallback and -persists every toggle. Docs sidebar sections/groups
carry data-key attributes and toggleCollapsible persists collapsed
state per key ('docs-nav-state'); restoreDocsNav() applies it at init —
server-rendered defaults still govern first visit.

make test green; rendering ownership OK (no new inline scripts); 146
vitests pass; live-verified SSR classes on 7 pages.

templates/index.templ

@@ -13,7 +13,7 @@ templ Index(loggedIn bool, registrationEnabled bool) {
 			<link href="/static/style.css" rel="stylesheet"/>
 			<link rel="icon" type="image/svg+xml" href="/static/favicon.svg"/>
 		</head>
-		<body class="theme-tokyo-night" x-data="index" x-init="initIndexTheme(); checkAuthRedirect()">
+		<body x-data="index" x-init="initIndexTheme(); checkAuthRedirect()">
 			<div class="absolute top-4 right-4 z-10">
 				<select
 					id="theme-select"