Add remote audio routing mode

[MuNeNiCK]

Summary

• add redirect/mirror/off audio mode selection with redirect as the default
• create a temporary PipeWire/Pulse remote sink for redirect mode and restore routing on stop/failure
• document and package the pactl dependency for AUR and Nix

Verification

• cargo fmt --check
• cargo test audio::routing:: -- --test-threads=1
• cargo test audio:: -- --test-threads=1
• cargo test -- --test-threads=1
• cargo clippy --all-targets -- -D warnings
• cargo build --release
• git diff --check
• bash -n pkg/aur/PKGBUILD && bash -n pkg/aur-git/PKGBUILD
• docker nix build .#hypr-rdp --no-link --print-build-logs