fix: support Windows TUI control

[matdev83]

Summary

• make OpenTUI host handling respond to standalone cursor-position reports used during OpenCode startup
• close the ConPTY master during Windows one-shot teardown and guard Unix-only EIO handling
• add Windows named-pipe transport for persistent single sessions while preserving Unix sockets on macOS/Linux
• update CLI help and README platform support notes

Root cause

OpenCode's TUI waits for a standalone CSI 6 n cursor-position response during startup. The host only replied as part of a larger OpenTUI capability probe. Persistent sessions were also compiled out on Windows because their control transport was implemented only with Unix sockets.

Impact

Windows can now launch and capture OpenCode through the PTY and orchestrate a persistent OpenCode TUI with start, show, send, wait, and stop. Unix and macOS continue using the existing Unix-socket implementation. Windows workspace attachment remains out of scope.

Validation

• cargo fmt --all -- --check
• cargo check --locked
• cargo test --locked --lib shot::tests (10 passed)
• live Windows persistent PowerShell input smoke test (GOT:HELLO)
• live persistent OpenCode TUI test: render UI, inject prompt using termctrl send, wait for ORCHESTRATED_TUI_OK, capture response, and stop cleanly