Add BorderBreaker - An Aspect Ratio Control Feature

[Draco-of-3000]

• Introduce a native AspectController that auto-detects ultrawide displays, cycles through nine modes (Auto, Fill, Fit, 16:9, 4:3, 1:1, 21:9, 32:9, Cinema), persists the last choice, and applies the correct MPV props immediately.
• Bind the B key globally (with focus guards) to send a borderbreaker-cycle RPC into Rust, so it works even when the Web UI has focus.
• Added a WebView-rendered toast that matches the Stremio design system (rounded, semi-transparent, auto-hide) to display aspect ratio mode when changed.

Testing:

• cargo test
• Manual: run stremio-runtime.exe server.js + cargo run -- --development --webui-url=https://web.stremio.com/?shell-dev --dev-tools, stream a video, verify:
• Auto mode fits a 21:9 monitor without pillar boxes.
• Pressing B cycles all modes, overlay text updates, and MPV aspect changes accordingly.
• Restart the app; previously selected mode loads from %APPDATA%\StremioBorderBreaker\aspect.json.