current_study_day_start_utc() passed use_space=true to
Time.get_datetime_string_from_unix_time(), producing "2026-07-21
00:00:00Z" (space separator) instead of ISO-8601. The server's
System.Text.Json DateTime converter rejects that with a 400, which
the client surfaces as a generic "could not be loaded" error -
blocking every study session. Confirmed against the live API: the
space-separated value 400s, the corrected T-separated value returns
a card.
Import and export were stubbed with status-text placeholders; wire them
to the existing backend endpoints with a real file picker (web JS
bridge or native FileDialog) and browser/desktop download, plus an
import preview with create/update/skip/error counts before commit.
Also fix the library and study screens' theme-refresh handlers, which
were no-op stubs so cards never restyled on a theme toggle, and add
responsive layout handling for narrow viewports.
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