StudySprint v0.3.0

Third versioned state: MINOR feature batch adding the
spaced-repetition module (FEATURES Next #1, issue #3050 as amended:
Obsidian vault surface included as a required component).

Provider credit: command-dispatch (Swarm Optimizations &
Implementation Assurance seat), session
6628d41d-9519-4881-9063-3afe501df815.

Added

• Spaced-repetition module (study_sr.py): cards built from the
  existing quiz/term data (practice-set q/a, question/answer, and
  term/definition shapes); two schedulers behind one interface,
  selectable by name — FSRS (default, via py-fsrs) and SM-2 (classic
  baseline). Every review returns a stamped receipt naming the
  scheduler that produced it; an unknown scheduler name raises a
  clear error.
• Anki export: export_apkg writes a genanki .apkg (deck
  "StudySprint") and returns a receipt with the file hash.
• Obsidian vault surface: export_obsidian_vault writes
  obsidian-spaced-repetition-format notes (sync state in
  frontmatter, #flashcards tag, front ? back) plus an index
  note; read_obsidian_card_state / import_obsidian_states read
  the state back (the vault -> core sync point). Device sync
  points (ObsidianBridge, push_cards_to_vault,
  pull_states_from_vault) adapt the fleet's existing adapter
  bin/obsidian_server.py (token-authenticated HTTP bridge, port
  8085, symlink-rejecting token read) — seeded from it, not a
  cold build.
• ts-fsrs UX seed: to_ts_fsrs_state / export_ux_state map
  py-fsrs card state onto the ts-fsrs Card shape for the UX layer.
• Tests: tests/test_study_sr.py covers every public function in
  study_sr.py.