chore: archive observability-service-registry, track pi-map artifacts

- Archive the completed observability-service-registry SDD change into
  openspec/changes/archive/ (delivered across 5 slices; only
  jellyfin-service-registry remains active).
- Stop ignoring .pi-map.md / .pi-map.index.md so the navigation maps are
  versioned alongside the code, and add the regenerated map pairs repo-wide.

monitoring/grafana/provisioning/dashboards-json/dashboards/.pi-map.index.md

@@ -0,0 +1,20 @@
+# monitoring/grafana/provisioning/dashboards-json/dashboards (index)
+dir: monitoring/grafana/provisioning/dashboards-json/dashboards
+
+## role
+This directory stores pre-built Grafana dashboard JSON definitions for monitoring the "manage" service and host-level system metrics via node-exporter.
+## parent
+index: monitoring/grafana/provisioning/dashboards-json/.pi-map.index.md
+map: monitoring/grafana/provisioning/dashboards-json/.pi-map.md
+## children
+-
+## files
+- manage-overview.json
+- node-exporter-overview.json
+## links
+index: monitoring/grafana/provisioning/dashboards-json/dashboards/.pi-map.index.md
+map: monitoring/grafana/provisioning/dashboards-json/dashboards/.pi-map.md
+## workflows
+-
+## dirty
+-

monitoring/grafana/provisioning/dashboards-json/dashboards/.pi-map.md

@@ -0,0 +1,20 @@
+# monitoring/grafana/provisioning/dashboards-json/dashboards
+dir: monitoring/grafana/provisioning/dashboards-json/dashboards
+
+index: monitoring/grafana/provisioning/dashboards-json/dashboards/.pi-map.index.md
+
+## role
+This directory stores pre-built Grafana dashboard JSON definitions for monitoring the "manage" service and host-level system metrics via node-exporter.
+## files
+- manage-overview.json | Grafana dashboard configuration for monitoring a "manage" service with metrics and logs visualization | dep: prometheus, loki, grafana
+- node-exporter-overview.json | Grafana dashboard JSON for visualizing node-exporter system metrics (CPU, memory, disk, network) | dep: Grafana, Prometheus, node-exporter
+## arch
+It follows Grafana's infrastructure-as-code provisioning pattern, using static JSON files to declaratively define dashboard layouts, queries, and visualizations that are automatically loaded by Grafana at startup.
+## tags
+grafana, overview, node, exporter, manage, dashboard, metrics, prometheus
+## symbols
+-
+## workflows
+-
+## dirty
+-