Phase 3 / M8: Add MIDI backend, parser, timing, CLI, and deterministic replay #13

Objective

Introduce isolated MIDI input and deterministic replay, converting timestamps into scheduler frames without requiring hardware in CI.

Scope

• Define backend/input/device/event interfaces and parsed note, CC, and pitch-bend messages.
• Implement robust MIDI byte parsing, including note-on velocity zero.
• Add Fedora ALSA sequencer input (or documented pinned backend), device enumeration, lifecycle, and disconnect events.
• Convert monotonic input timestamps using audio-clock snapshots and configurable latency compensation.
• Apply late events at the earliest available frame and report lateness; use bounded queues with explicit overflow.
• Implement deterministic timestamped replay logs.
• Add lgs midi list [--json], monitor, replay, and doctor integration.
• Add parser fuzzing, virtual/replay tests, statistics/traces, and Fedora behavior documentation.

Acceptance criteria

• Replay produces identical converted frames headlessly and malformed input cannot crash the process.
• Device enumeration works when MIDI devices are available; missing hardware does not fail acceptance.
• Late/drop/overflow behavior is explicit and observable.

Spec: phase-3.md §§20, 22, 26, 30, 32–36, 39–40 (Milestone 8), 42.