Crossword Puzzle

# Crossword Puzzle PRD

## Overview
Build a crossword puzzle game that generates playable grids from word and clue pairs, with interactive cell navigation, hint and validation systems, and multiple pre-built puzzles.

## Requirements
- Generate a crossword grid layout from a list of word and clue pairs
- Numbered cells for across and down clues following standard crossword conventions
- Click a cell to select it and begin typing
- Type to fill in letters one at a time advancing through the word
- Tab key to jump to the next word in sequence
- Toggle between across and down direction when clicking an already-selected cell
- Clue panel displayed alongside the grid listing all across and down clues
- Highlight the current word in the grid as the player types
- Highlight the current clue in the clue list panel
- Check a single letter for correctness (via right-click or a check button)
- Check the entire puzzle for correctness with error indicators
- Reveal letter or reveal word hint buttons
- Timer tracking how long the player has been solving
- Error highlighting with red background for incorrect letters
- Pencil mode that marks uncertain letters in a different style (e.g., lighter color)
- Clear puzzle button to reset all entered letters
- Completion detection with a celebration animation when the puzzle is solved
- Print-friendly layout for solving on paper
- Responsive design for desktop and mobile
- Include at least 3 pre-built puzzles with varying difficulty

## Tech Stack
- HTML, CSS, JavaScript (vanilla or any framework)
- No crossword generation libraries — build the grid layout algorithm yourself

## Scoring Criteria
- **Functional (40%)**: Grid generation works, cell navigation and typing work, clues display correctly
- **Quality (20%)**: Clean code, smooth keyboard navigation, handles edge cases (overlapping words, empty cells)
- **Fidelity (25%)**: All features implemented including hints, pencil mode, timer, print layout, pre-built puzzles
- **Speed (15%)**: Time bonus