feat: minimize manager to system tray

[Peterpan0315]

Summary

• Based on BigPizzaV3/CodexPlusPlus v1.1.8.
• Adds a Windows system tray workflow for Codex++ Manager: window close hides to tray, tray left-click restores the window, and tray menu exposes Open and Exit.
• Documents the fork-specific tray feature in README and TRAY_FEATURE.md.

Test Plan

• npm run check
• npm run vite:build
• cargo test -p codex-plus-manager --test windows_subsystem manager_close_button_minimizes_to_system_tray
• cargo build -p codex-plus-manager --release --bin codex-plus-plus-manager