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/.pi-map.index.md

@@ -0,0 +1,44 @@
+# frontend/src/components (index)
+dir: frontend/src/components
+
+## role
+React UI component library providing reusable display elements, dashboard widgets, and page-level views for backup management, observability, media sessions, and widget configuration.
+## parent
+index: frontend/src/.pi-map.index.md
+map: frontend/src/.pi-map.md
+## children
+- frontend/src/components/__tests__
+  index: frontend/src/components/__tests__/.pi-map.index.md
+  map: frontend/src/components/__tests__/.pi-map.md
+- frontend/src/components/ui
+  index: frontend/src/components/ui/.pi-map.index.md
+  map: frontend/src/components/ui/.pi-map.md
+## files
+- BackupAlertsTable.tsx
+- BackupDashboardWidget.tsx
+- BackupJobsTable.tsx
+- BackupRunsTable.tsx
+- BackupsPage.tsx
+- ConfirmDialog.tsx
+- DialogFooter.tsx
+- HoverEditButton.tsx
+- LibraryOverview.tsx
+- MetricCard.tsx
+- NowPlaying.tsx
+- ObservabilityPage.tsx
+- SectionCard.tsx
+- SelectionRailCard.tsx
+- SessionActivityPanel.tsx
+- TabbedCard.tsx
+- WidgetConfigDialog.tsx
+- WidgetInstance.tsx
+## links
+index: frontend/src/components/.pi-map.index.md
+map: frontend/src/components/.pi-map.md
+## workflows
+- change components behavior
+  read: BackupAlertsTable.tsx, BackupDashboardWidget.tsx, BackupJobsTable.tsx
+- explore components subdirectories
+  index: frontend/src/components/__tests__/.pi-map.index.md, frontend/src/components/ui/.pi-map.index.md
+## dirty
+-