feat(monitoring): add GlitchTip health check and disk space monitoring

- Add GlitchTip to health-check.sh monitoring endpoints
- Add native disk space checks for / and /Volumes/ManaData with 80%/90% thresholds
- Extend Prometheus disk alerts to include /host_mnt/Volumes/ManaData mountpoint
- Add ManaData disk usage gauge to Grafana system-overview dashboard

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/mac-mini/health-check.sh

@@ -273,6 +273,7 @@ echo ""
 echo "Monitoring:"
 check_service "Grafana" "http://localhost:8000/api/health"
 check_service "Umami" "http://localhost:8010/api/heartbeat"
+check_service "GlitchTip" "http://localhost:8020/_health/"
 check_service "VictoriaMetrics" "http://localhost:9090/health"
 
 echo ""
@@ -281,6 +282,36 @@ check_service "vmalert" "http://localhost:8880/health"
 check_service "Alertmanager" "http://localhost:9093/-/healthy"
 check_service "Alert Notifier" "http://localhost:9095/health"
 
+echo ""
+echo "Disk Space:"
+check_disk() {
+    local name=$1
+    local path=$2
+    local warn_pct=${3:-80}
+    local crit_pct=${4:-90}
+
+    if [ ! -d "$path" ]; then
+        echo -e "  ${YELLOW}[SKIP]${NC} $name ($path not found)"
+        return 0
+    fi
+
+    local usage_pct=$(df "$path" | tail -1 | awk '{gsub(/%/,""); print $5}')
+    local avail=$(df -h "$path" | tail -1 | awk '{print $4}')
+
+    if [ "$usage_pct" -ge "$crit_pct" ]; then
+        echo -e "  ${RED}[CRIT]${NC} $name: ${usage_pct}% used ($avail free)"
+        FAILURES+=("Disk $name: ${usage_pct}% (critical)")
+    elif [ "$usage_pct" -ge "$warn_pct" ]; then
+        echo -e "  ${YELLOW}[WARN]${NC} $name: ${usage_pct}% used ($avail free)"
+        FAILURES+=("Disk $name: ${usage_pct}% (warning)")
+    else
+        echo -e "  ${GREEN}[OK]${NC} $name: ${usage_pct}% used ($avail free)"
+    fi
+}
+
+check_disk "System (/)" "/"
+check_disk "ManaData" "/Volumes/ManaData"
+
 echo ""
 echo "Cloudflare Tunnel:"
 if pgrep -x "cloudflared" >/dev/null; then