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.

frontend/src/integrations/.pi-map.index.md

@@ -0,0 +1,23 @@
+# frontend/src/integrations (index)
+dir: frontend/src/integrations
+
+## role
+Frontend integration layer that maps backend service types and widgets to their corresponding React components, metadata, and configuration schemas.
+## parent
+index: frontend/src/.pi-map.index.md
+map: frontend/src/.pi-map.md
+## children
+-
+## files
+- registry.test.ts
+- registry.ts
+## links
+index: frontend/src/integrations/.pi-map.index.md
+map: frontend/src/integrations/.pi-map.md
+## workflows
+- change integrations behavior
+  read: registry.ts
+- update integrations tests
+  read: registry.test.ts
+## dirty
+-