Use pywinpty instead of ptyprocess on Windows for PTY support

ptyprocess depends on Unix-only APIs (fork, openpty) and cannot work
on Windows at all. pywinpty provides a compatible PtyProcess interface
using the Windows ConPTY API.

This conditionally imports winpty.PtyProcess on Windows and
ptyprocess.PtyProcess on Unix. The pyproject.toml pty extra now uses
platform markers so the correct package is installed automatically.

pyproject.toml

@@ -45,7 +45,10 @@ cron = ["croniter"]
 slack = ["slack-bolt>=1.18.0", "slack-sdk>=3.27.0"]
 cli = ["simple-term-menu"]
 tts-premium = ["elevenlabs"]
-pty = ["ptyprocess>=0.7.0"]
+pty = [
+  "ptyprocess>=0.7.0; sys_platform != 'win32'",
+  "pywinpty>=2.0.0; sys_platform == 'win32'",
+]
 honcho = ["honcho-ai>=2.0.1"]
 mcp = ["mcp>=1.2.0"]
 homeassistant = ["aiohttp>=3.9.0"]