Rework app bar, notes layout, Settings/Admin/login restyle

App bar: brand, Studies / Read Bible / Reading Plans, and one account menu
(theme, Settings, Admin, Log out). Study stage: notes get their own box above
the resources in the right column. Settings, Admin and the login page use the
reader themes; add a theme-aware danger colour.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/components/study/StudioShell.jsx

@@ -48,7 +48,7 @@ export default function StudioShell({ stage, loading = false, fixedHeight = fals
                 : syncStatus === 'syncing' ? <span>Syncing…</span>
                   : syncStatus === 'synced' ? <span>Saved</span>
                     : syncStatus === 'error' ? (
-                      <span className="text-red-600">Sync failed <button type="button" onClick={retrySync} className="underline">Retry</button></span>
+                      <span className="text-[var(--r-danger,#b42318)]">Sync failed <button type="button" onClick={retrySync} className="underline">Retry</button></span>
                     ) : null}
             <button type="button" onClick={cycleTheme} className="rounded-lg px-2 py-1 hover:bg-black/5" title="Change theme">{READER_THEMES[readerTheme]?.label}</button>
           </div>