feat: Add WebSocket playground for real-time API testing

[hkdeman]

Implement comprehensive WebSocket playground component with real-time connection management

Summary

• Add WebSocket playground component with real-time messaging capabilities
• Support for custom headers, subprotocols, and multiple server endpoints
• Message history with timestamps and connection status indicators
• Consistent UI/UX with existing HTTP playground

Test plan

• Test WebSocket connection to echo server
• Verify message sending and receiving
• Test custom headers and subprotocols
• Verify connection status indicators
• Test multiple server endpoints
• Test binary message support

Closes #26

🤖 Generated with Claude Code

[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
Potential XSS vulnerability in binary message handling	Medium	Set the message type to "binary". Enter a string containing HTML or JavaScript code, such as <img src=x onerror=alert(1)>. Click "Send".	The sendMessage function, when handling binary messages, encodes the messageInput string using TextEncoder and sends the resulting ArrayBuffer to the WebSocket server. However, the received message is then displayed in the message history without proper sanitization. This could lead to a stored XSS vulnerability if the server echoes the binary data back to the client, as the client-side code then displays the unsanitized binary data as text in the message history.

_{Comments? Email us.}