Apply the real frosted .glass surface (blur) to the few large chrome surfaces — the nav
sidebar, the header and all Modal-based dialogs (was glass-card / plain surfaces) — and
enrich the ambient backdrop a touch (three soft accent pools) so the glass has more to
refract app-wide. Popovers (notifications, language, account, add-to-playlist) were
already glass. Bulk feed cards stay glass-card (no per-card blur) for performance; the
existing perf-mode still disables blur. Phase 2 (ambient thumbnail mosaic / bg image +
toggle) deferred to end-of-project polish.