Implementation Requirements

Requires Issue Implement Check Detection System #76 (Check Detection System) to be implemented first, as this feature needs the is_in_check(color) method to determine when a king is in check.

Extend game state JSON response to include check status:
- Add inCheck field indicating which color (if any) is currently in check
- Example: { "inCheck": "light" } or { "inCheck": null }
Update WebSocket message handling to include check status after every move validation and board state update

Update chess.js composable to track check state:
- Parse the inCheck field from the game state
- Expose a reactive kingInCheck variable (or similar) for components to consume
Update Tile.vue component to apply check styling:
- Add conditional class binding for when the tile contains a king that is in check
- Example: :class="{ 'in-check': isKingInCheck }"
Update Piece.vue component (if separate) to visually indicate the king is in check:
- Apply red highlight or border to the king piece itself

Define .in-check class for the square:
- Red background color or red border/glow effect
- Consider using box-shadow for a glow effect: box-shadow: inset 0 0 20px rgba(255, 0, 0, 0.6)
- Alternatively, a semi-transparent red overlay
Optional: Add animation for better visibility:
- Subtle pulsing animation to draw attention to the checked king
- Example: @keyframes pulse-red { 0%, 100% { opacity: 0.6; } 50% { opacity: 0.9; } }

When a move puts the opponent's king in check, the king's square turns red
The red highlight is removed when the check is resolved (king moves, piece blocks, or attacker is captured)
Works for both white and black kings
Visual indication is clear and noticeable without being distracting
Check state updates in real-time after each move

Implement Check Detection System #76 - Check Detection System (prerequisite)
Check/Checkmate/Pinning Implementation #72 - Check/Checkmate/Pinning Implementation

Indicate when a king is in check #80