Rust-based CLI music visualiser

refactor: extract app session runtime from main #1

Merged sigilzero.dev
targeting main from feat/portability-runtime
Merged opened by and assigned to sigilzero.dev
targeting main from feat/portability-runtime

Refactor various program state handling into a proper app module.

Also improve audio source management, and compatibility with other terminal colourschemes and character sets

Commits 6

docs: trim the readme
refactor: extract app session runtime from main
feat: add Pulse fallback and display docs
build: add toolchain and Nix checks
refactor: centralise scene registry and routing
feat: add portable audio sources and terminal controls