- Create ThemeSessionBridge.tsx: useEffect compares session.user.theme to
next-themes value; calls setTheme(serverTheme) on mismatch; validates
against 3-string allowlist ('light'|'dark'|'system'); renders null
- Mount <ThemeSessionBridge /> as first child of <AuthProvider> in app/layout.tsx
- Modify ThemeToggle: writeTheme() calls setTheme() then fire-and-forget
PUT /api/me/theme; silent catch for network errors (best-effort desktop UX)
