Linux TTY screen reader interop (out of scope for PoC)

[digitalby]

Tracking issue for Linux TTY interop. The user explicitly asked for this to be out of scope for the PoC and tracked here.

The Linux console already has workable screen readers: emacspeak, speakup (kernel TTY), fenrir (PTY driver), BRLTTY for braille. The question is whether `acc` should:

1. Detect a running fenrir/emacspeak/speakup and defer to it (no-op backend, let the existing reader handle Claude Code's output directly)
2. Emit events to speech-dispatcher instead of driving spd-say ad-hoc
3. Stay out of the way entirely on Linux and focus on macOS where no console reader exists

Not blocking the PoC. Revisit once macOS + Windows flows are solid.