Both are still in progress and shouldn't be reachable in production
(or local dev) yet - hide every entry point (nav sidebar, the
dashboard's "dynamic concepts due" review card, and the CCS Cases
mode card on the study selector) unless step3/deployment_environment
is "uat", the same setting that already drives the UAT badge. Added
Brand.is_uat_environment() as the shared check.
Adds a full flashcards system: FSRS-based scheduling, cloze/basic
card types, CSV import/export, media storage, and study UI, wired
into navigation and the dashboard alongside existing question flows.
hz