Export flashcards/notes to Anki (and similar retention tools)

[nazim117]

Problem

Once flashcards exist (#61), people already have muscle memory and existing decks in dedicated spaced-repetition tools — Anki being the standard. Without export, this becomes a second, disconnected place to review.

Proposal

Add an export path for flashcards (and optionally structured notes) to Anki's package format (.apkg) at minimum; Obsidian/Notion-friendly markdown export could follow as a lower-priority stretch.

Depends on

• Add flashcards + spaced repetition for active recall #61 (flashcards/spaced repetition) — nothing to export until that exists.