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/superpowers/.pi-map.md

@@ -0,0 +1,18 @@
+# docs/superpowers
+dir: docs/superpowers
+
+index: docs/superpowers/.pi-map.index.md
+
+## role
+Documentation directory for advanced features, capabilities, or customization guides within the project.
+## files
+## arch
+Flat-file documentation structure (currently empty of content files), serving as a namespace for specialized or extended documentation topics.
+## tags
+-
+## symbols
+-
+## workflows
+-
+## dirty
+-