Add tracing and FIFO PCM sink support
Initialize tracing_subscriber in CLI components and replace
println!/eprintln! calls with tracing macros across crates. Add
tracing/tracing-subscriber to workspace deps. Introduce sys bindings
and helpers (pcm_switch_sink, pcm_fifo_set_path) and NewGlobalSettings
fields (audio_output, fifo_path). Wire settings to switch to a FIFO
PCM sink on startup, expose FIFO sink in firmware headers, and include
hosted pcm-fifo.c in the build.