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.

archive/src/media_library_viewer/clients/.pi-map.index.md

@@ -0,0 +1,23 @@
+# archive/src/media_library_viewer/clients (index)
+dir: archive/src/media_library_viewer/clients
+
+## role
+External service and system integration layer providing HTTP API clients for Jellyfin/Emby media servers and SSH-based remote system metrics collection.
+## parent
+index: archive/src/media_library_viewer/.pi-map.index.md
+map: archive/src/media_library_viewer/.pi-map.md
+## children
+-
+## files
+- __init__.py
+- jellyfin.py
+- resources.py
+- ssh.py
+## links
+index: archive/src/media_library_viewer/clients/.pi-map.index.md
+map: archive/src/media_library_viewer/clients/.pi-map.md
+## workflows
+- change clients behavior
+  read: __init__.py, jellyfin.py, resources.py
+## dirty
+-