midi-bridge: add prometheus metrics on :9091/metrics

- midi_messages_total: all MIDI messages
- midi_notes_on/off_total: note-on/off counts
- midi_last_status/note/velocity: last message tokens
- midi_last_time_unix: epoch of last message
- Removed MIDI counters from prometheus-exporter (bridge owns them)

scripts/prometheus-exporter.py

@@ -11,11 +11,6 @@ SSH_KEY = os.environ.get("SSH_KEY", "/home/david/.ssh/unoq_deploy_key")
 BOARD = os.environ.get("BOARD_HOST", "127.0.0.1")
 COLLECT_INTERVAL = 5  # seconds between metric collections
 
-# ── Counters ──
-midi_notes_on = 0
-midi_notes_off = 0
-midi_errors = 0
-
 # ── Gauges (updated by collector) ──
 metrics = {
     "synth_alsa_running": 0,
@@ -119,18 +114,6 @@ def collect_metrics():
 
 def format_metrics():
     lines = []
-    lines.append("# HELP synth_midi_notes_on_total Total MIDI note-on messages received")
-    lines.append("# TYPE synth_midi_notes_on_total counter")
-    lines.append(f"synth_midi_notes_on_total {midi_notes_on}")
-
-    lines.append("# HELP synth_midi_notes_off_total Total MIDI note-off messages received")
-    lines.append("# TYPE synth_midi_notes_off_total counter")
-    lines.append(f"synth_midi_notes_off_total {midi_notes_off}")
-
-    lines.append("# HELP synth_midi_errors_total Total MIDI parse errors")
-    lines.append("# TYPE synth_midi_errors_total counter")
-    lines.append(f"synth_midi_errors_total {midi_errors}")
-
     lines.append("# HELP synth_alsa_running Whether ALSA device is RUNNING")
     lines.append("# TYPE synth_alsa_running gauge")
     lines.append(f"synth_alsa_running {metrics['synth_alsa_running']}")