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/ui/.pi-map.index.md

@@ -0,0 +1,46 @@
+# frontend/src/components/ui (index)
+dir: frontend/src/components/ui
+
+## role
+Reusable, design-system UI component library providing styled, accessible primitives (buttons, inputs, dialogs, tables, etc.) for consistent application interfaces.
+## parent
+index: frontend/src/components/.pi-map.index.md
+map: frontend/src/components/.pi-map.md
+## children
+- frontend/src/components/ui/__tests__
+  index: frontend/src/components/ui/__tests__/.pi-map.index.md
+  map: frontend/src/components/ui/__tests__/.pi-map.md
+## files
+- alert.tsx
+- avatar.tsx
+- badge.tsx
+- button.tsx
+- card.tsx
+- checkbox.tsx
+- collapsible.tsx
+- data-table.tsx
+- dialog.tsx
+- dropdown-menu.tsx
+- input.tsx
+- label.tsx
+- progress.tsx
+- scroll-area.tsx
+- select.tsx
+- separator.tsx
+- sheet.tsx
+- skeleton.tsx
+- switch.tsx
+- table.tsx
+- tabs.tsx
+- textarea.tsx
+- tooltip.tsx
+## links
+index: frontend/src/components/ui/.pi-map.index.md
+map: frontend/src/components/ui/.pi-map.md
+## workflows
+- change ui behavior
+  read: alert.tsx, avatar.tsx, badge.tsx
+- explore ui subdirectories
+  index: frontend/src/components/ui/__tests__/.pi-map.index.md
+## dirty
+-