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/.pi-map.index.md

@@ -0,0 +1,47 @@
+# frontend (index)
+dir: frontend
+
+## role
+React-based single-page application frontend for the "Manage" project, providing the user interface with Vite tooling, Tailwind CSS styling, and OIDC authentication.
+## parent
+index: ./.pi-map.index.md
+map: ./.pi-map.md
+## children
+- frontend/public
+  index: frontend/public/.pi-map.index.md
+  map: frontend/public/.pi-map.md
+- frontend/src
+  index: frontend/src/.pi-map.index.md
+  map: frontend/src/.pi-map.md
+- frontend/tests
+  index: frontend/tests/.pi-map.index.md
+  map: frontend/tests/.pi-map.md
+## files
+- .gitignore
+- Dockerfile
+- README.md
+- components.json
+- eslint.config.js
+- index.html
+- nginx.conf
+- package-lock.json
+- package.json
+- postcss.config.cjs
+- tailwind.config.cjs
+- tsconfig.app.json
+- tsconfig.json
+- tsconfig.node.json
+- vite.config.ts
+- vitest.config.ts
+## links
+index: frontend/.pi-map.index.md
+map: frontend/.pi-map.md
+## workflows
+- change frontend behavior
+  read: .gitignore, Dockerfile, eslint.config.js
+- change frontend config
+  read: components.json, eslint.config.js, package-lock.json
+- explore frontend subdirectories
+  index: frontend/public/.pi-map.index.md, frontend/src/.pi-map.index.md, frontend/tests/.pi-map.index.md
+## dirty
+-