Expose typed terminal input without an actor scheduler

[wolfy-j]

Compiled terminal clients need parsed input without creating a scheduler-owned process solely to receive keystrokes, plus a completion signal when the terminal disconnects. The former Unix reader parsed each read independently, so terminal sequences split at a buffer boundary could be corrupted.

This change exposes NewEventInputReader with serial typed callbacks while preserving NewInputReader as the scheduler adapter. Each session reports Done and Err, late cleanup cannot stop a restarted reader, and Stop restores terminal modes while serializing cleanup.

Unix input now uses the existing streaming decoder with a bounded incomplete-frame budget. The polished replay removes unrelated test commits, correctly releases accounting for completed multi-read events, and handles decoder-channel closure without spinning. Windows retains the established Console API reader.

Validation: the terminal service suite passes under race; framing and shutdown regressions pass repeatedly; repository-pinned scoped lint, vet, Windows compilation, and diff checks pass. Coverage includes fragmented mouse and navigation sequences, UTF-8 and paste input, EOF with data, framing bounds, restart generations, cancellation, and consecutive large valid pastes.