Extract casting functionality (Chromecast, AirPlay, DLNA) to standalone
qbz-cast crate. This crate is Tauri-agnostic and can be used by TUI/CLI
clients.
- Move device connection, discovery, threading, and media server to crate
- Keep only Tauri commands in src-tauri/src/cast/
- Thin re-exports in src-tauri for backwards compatibility
- Remove duplicate dependencies from src-tauri Cargo.toml
vicrodh