Typing Speed Test

# Typing Speed Test PRD

## Overview
Build a typing speed test application that measures words per minute and accuracy with multiple text modes, real-time feedback, and personal best tracking.

## Requirements
- Display a text passage for the user to type
- Real-time WPM (words per minute) calculation updated as the user types
- Accuracy percentage showing correct characters vs total typed
- Highlight the current word being typed
- Color correct characters green and incorrect characters red
- Multiple test durations: 15 seconds, 30 seconds, 60 seconds, 120 seconds
- Different text modes: famous quotes, paragraphs, code snippets, random common words
- Show a live WPM line chart during the test (updates every second)
- Results screen showing: final WPM, accuracy, time elapsed, total characters typed
- Personal best tracking saved to localStorage (best WPM per duration)
- Restart with the same text or generate new text
- Focus mode that dims already-completed text for less distraction
- Character-level error highlighting (show exactly which characters were wrong)
- Display both raw WPM and adjusted WPM (penalized for errors)

## Tech Stack
- HTML, CSS, JavaScript (vanilla or any framework)
- Canvas or SVG for the live WPM chart (no charting libraries)

## Scoring Criteria
- **Functional (40%)**: Typing detection works, WPM calculation accurate, timer functions correctly
- **Quality (20%)**: Smooth real-time updates, accurate metrics, clean code
- **Fidelity (25%)**: All features present including live chart, text modes, personal bests
- **Speed (15%)**: Time bonus