feat: Follower Mode (External Master)

[ElBeh]

Description

Second operating mode where SongLab follows an external device (e.g. M-Live
B.Beat, DAW, or any MIDI-capable playback system) instead of controlling
playback itself. The external device is the audio master; SongLab acts as a
passive "digital music stand".

Depends on: MIDI Input (#10)
Estimated effort: ~4–6h (on top of MIDI Input feature)

Requirements

Mode switching

• Mode toggle in settings or toolbar (Master / Follower)
• Follower mode: transport controls disabled or hidden
• Follower mode: no local audio playback
• Follower mode: DummyWaveform component with simulated playhead (optional)
• Visual indicator showing current mode and connection status
• Mode persisted in localStorage

MIDI-driven navigation (Follower mode)

• Incoming Program Change → switch to song N in active setlist
• Incoming CC (configurable) → jump to section by index
• Incoming CC → Play/Stop signal (update UI state without audio)
• Optional: MIDI Clock sync for continuous position tracking (future)
• Optional: MIDI Timecode (MTC) for sample-accurate position (future)

Band Sync integration

• Host in Follower mode: MIDI-triggered song/section changes forwarded to all viewers via existing WebSocket sync protocol
• Chain: B.Beat → MIDI → SongLab Host (Follower) → WebSocket → Viewers
• Viewers behave identically regardless of Host mode (transparent)

Decisions

• Follower mode reuses DummyWaveform component (no audio, visual timeline only)
• Initial version uses discrete MIDI messages (PC/CC) only. Continuous position sync via MIDI Clock/MTC deferred
• Architecturally similar to Band Sync Viewer but driven by MIDI instead of WebSocket
• B.Beat's proprietary WiFi/Prompter protocol is not supported (closed system)