feat: replace desktop QA popup with egui

[aeoform]

Summary

• replace the desktop selection QA WebView popup with a native egui popup on Linux, Windows, and macOS
• keep the egui selection-polish preview Linux-only while Windows and macOS retain the existing WebView path
• embed popup mode in the main executable and communicate through JSON lines over stdin/stdout
• restore the original QA layout behavior, selected-text envelope presentation, right-aligned user messages, Markdown rendering, wrapping, rounded corners, dragging, and Escape dismissal
• keep the recording composer and selection context inside fixed window bounds

Validation

• cargo check --bin openless --bin egui_popup
• cargo build --release --bin openless
• manually tested the Linux QA and selection-polish popup flows

Platform note

The current development environment only has the Linux Rust target installed. Linux was compiled and manually exercised; Windows and macOS routing is implemented but was not cross-compiled locally.