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/.pi-map.index.md

@@ -0,0 +1,32 @@
+# monitoring (index)
+dir: monitoring
+
+## role
+Provides observability, metrics collection, and health-checking capabilities for the application.
+## parent
+index: ./.pi-map.index.md
+map: ./.pi-map.md
+## children
+- monitoring/alertmanager
+  index: monitoring/alertmanager/.pi-map.index.md
+  map: monitoring/alertmanager/.pi-map.md
+- monitoring/alloy
+  index: monitoring/alloy/.pi-map.index.md
+  map: monitoring/alloy/.pi-map.md
+- monitoring/grafana
+  index: monitoring/grafana/.pi-map.index.md
+  map: monitoring/grafana/.pi-map.md
+- monitoring/loki
+  index: monitoring/loki/.pi-map.index.md
+  map: monitoring/loki/.pi-map.md
+- monitoring/prometheus
+  index: monitoring/prometheus/.pi-map.index.md
+  map: monitoring/prometheus/.pi-map.md
+## files
+## links
+index: monitoring/.pi-map.index.md
+map: monitoring/.pi-map.md
+## workflows
+-
+## dirty
+-