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.

docs/.pi-map.index.md

@@ -0,0 +1,24 @@
+# docs (index)
+dir: docs
+
+## role
+Documentation package containing architectural plans, requirements, and operational guides for the "Manage" media library application and its observability stack.
+## parent
+index: ./.pi-map.index.md
+map: ./.pi-map.md
+## children
+- docs/superpowers
+  index: docs/superpowers/.pi-map.index.md
+  map: docs/superpowers/.pi-map.md
+## files
+- MIGRATION_PLAN.md
+- REQUIREMENTS.md
+- monitoring-logging-design.md
+- observability-runbooks.md
+## links
+index: docs/.pi-map.index.md
+map: docs/.pi-map.md
+## workflows
+-
+## dirty
+-