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/lib/.pi-map.index.md

@@ -0,0 +1,20 @@
+# frontend/src/lib (index)
+dir: frontend/src/lib
+
+## role
+Provides shared utility functions for the frontend application.
+## parent
+index: frontend/src/.pi-map.index.md
+map: frontend/src/.pi-map.md
+## children
+-
+## files
+- utils.ts
+## links
+index: frontend/src/lib/.pi-map.index.md
+map: frontend/src/lib/.pi-map.md
+## workflows
+- change lib behavior
+  read: utils.ts
+## dirty
+-

frontend/src/lib/.pi-map.md

@@ -0,0 +1,22 @@
+# frontend/src/lib
+dir: frontend/src/lib
+
+index: frontend/src/lib/.pi-map.index.md
+
+## role
+Provides shared utility functions for the frontend application.
+## files
+- utils.ts | Utility function that merges Tailwind CSS classes with proper deduplication and conflict resolution | exp: func:cn(...inputs: ClassValue[]), call:twMerge, call:clsx | dep: clsx, tailwind-merge
+## arch
+Functional utility module pattern leveraging clsx and tailwind-merge for deterministic CSS class composition.
+## tags
+merge, tailwind, cn, call:tw, call:clsx, utils, utility, merges
+## symbols
+- cn
+- call:twMerge
+- call:clsx
+## workflows
+- change lib behavior
+  read: utils.ts
+## dirty
+-