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/components/__tests__/.pi-map.index.md

@@ -0,0 +1,32 @@
+# frontend/src/components/__tests__ (index)
+dir: frontend/src/components/__tests__
+
+## role
+Test suite providing unit test coverage for reusable UI components and feature widgets in the frontend.
+## parent
+index: frontend/src/components/.pi-map.index.md
+map: frontend/src/components/.pi-map.md
+## children
+-
+## files
+- BackupAlertsTable.test.tsx
+- BackupDashboardWidget.test.tsx
+- BackupRunsTable.test.tsx
+- ConfirmDialog.test.tsx
+- DialogFooter.test.tsx
+- HoverEditButton.test.tsx
+- LibraryOverview.test.tsx
+- MetricCard.test.tsx
+- NowPlaying.test.tsx
+- SectionCard.test.tsx
+- SelectionRailCard.test.tsx
+- SessionActivityPanel.test.tsx
+- TabbedCard.test.tsx
+## links
+index: frontend/src/components/__tests__/.pi-map.index.md
+map: frontend/src/components/__tests__/.pi-map.md
+## workflows
+- update __tests__ tests
+  read: BackupAlertsTable.test.tsx, BackupDashboardWidget.test.tsx, BackupRunsTable.test.tsx
+## dirty
+-