Add PTY (pseudo-terminal) API documentation

Adds comprehensive documentation for the new PTY support feature from
PR #310 (cloudflare/sandbox-sdk#310).

New documentation includes:
- Complete PTY API reference with all methods (create, attach, getById, list, etc.)
- PTY handle interface documentation (write, resize, kill, onData, onExit)
- Transport options (HTTP vs WebSocket)
- When to use PTY vs Commands
- Complete examples with xterm.js integration
- Best practices and error handling patterns
- Terminal configuration guide

Also updates the API index page to include the PTY card in the navigation.

Author: github-actions[bot]

src/content/docs/sandbox/api/index.mdx

@@ -27,6 +27,14 @@ The Sandbox SDK provides a comprehensive API for executing code, managing files,
 	Execute commands and stream output. Run scripts, manage background processes, and capture execution results.
 </LinkTitleCard>
 
+<LinkTitleCard
+	title="PTY (Pseudo-Terminal)"
+	href="/sandbox/api/pty/"
+	icon="seti:shell"
+>
+	Create interactive terminal sessions with full PTY support for terminal-based applications requiring ANSI codes and bidirectional I/O.
+</LinkTitleCard>
+
 <LinkTitleCard
 	title="Files"
 	href="/sandbox/api/files/"