Flashcard App

# Flashcard App PRD

## Overview
Build a flashcard study application that lets users create decks, study cards with flip animations, and uses spaced repetition to optimize learning.

## Requirements
- Create decks with a title and description
- Add cards to decks with front (question) and back (answer) text
- Flip animation on click or tap to reveal the answer
- Mark each card as "know" or "don't know" after flipping
- Shuffle deck to randomize card order
- Progress tracking showing cards mastered vs remaining in current session
- Spaced repetition algorithm: show missed cards more frequently than mastered ones
- Edit and delete individual cards within a deck
- Import cards from CSV or JSON file format
- Export deck as JSON file download
- Search across all cards in all decks by front or back text
- Keyboard navigation: Space to flip, Right arrow for "know", Left arrow for "don't know"
- Deck statistics: mastery percentage, number of study sessions, cards due for review
- Persist all data (decks, cards, progress) to localStorage

## Tech Stack
- HTML, CSS, JavaScript (vanilla or any framework)
- CSS transitions or animations for card flip effect

## Scoring Criteria
- **Functional (40%)**: Card creation works, flip animation works, know/don't know tracking works
- **Quality (20%)**: Smooth animations, spaced repetition logic is sound, clean code
- **Fidelity (25%)**: All features present including import/export, search, statistics
- **Speed (15%)**: Time bonus