Add macOS and Windows cross-platform session bridge

[streetlightstartupnotes]

What changed

• preserve the existing macOS Swift Accessibility single-send bridge
• add a Windows C# UI Automation bridge loaded through Windows PowerShell
• route native sends automatically by operating system without adding a second app-server turn
• add Windows start, stop, and privacy-safe diagnostic scripts
• add Windows path handling, platform-aware status text, setup guidance, and a real-device test checklist
• add macOS and Windows GitHub Actions checks

Why

The browser grid must control the same Codex Session on macOS and Windows while submitting each user message exactly once. The Windows implementation mirrors the macOS contract: open the target task, fill the native composer, submit once, then let the grid poll the same Session.

Validation

• macOS alternate-port smoke test returned version 0.2.0-beta.1 and platform macos
• Codex app-server thread listing succeeded
• existing Swift bridge probe remained trusted
• Node syntax, shell syntax, Swift type-check, plugin validation, skill validation, YAML parsing, diff checks, and sensitive-data scan passed
• Windows PowerShell parsing and C# UI Automation compilation are covered by the new windows-latest workflow

Manual test still required

A real interactive Windows 11 desktop is still required to confirm the current Codex/ChatGPT App UI Automation element names and the codex:// task deep link. Follow docs/WINDOWS_TESTING.md and confirm that one web send produces exactly one App message and one Session response.