add boot-time synth-diagnostic.service

- synth-diagnostic.service: runs test-unit.py before pipeline services
- Type=oneshot, After=prometheus-exporter, Before=pipeline services
- Pipeline services: After=synth-diagnostic
- deploy: restart prometheus-exporter → start synth-diagnostic → restart pipeline
- install.sh: includes synth-diagnostic in SERVICES array

scripts/run-tests.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# run-tests.sh — wrapper for test-unit.py with exit code mapping
+set -euo pipefail
+
+BOARD="${BOARD_HOST:-192.168.9.167}"
+cd /home/arduino/uno-q-audio-synth
+
+echo "[diag] Running synth pipeline diagnostics against $BOARD..."
+
+python3 scripts/test-unit.py "$BOARD"
+exit_code=$?
+
+if [ $exit_code -eq 0 ]; then
+    echo "[diag] All tests PASSED — pipeline healthy"
+else
+    echo "[diag] Tests FAILED (exit $exit_code) — check dashboard for details"
+fi
+
+exit $exit_code