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/public/.pi-map.md

@@ -0,0 +1,20 @@
+# frontend/public
+dir: frontend/public
+
+index: frontend/public/.pi-map.index.md
+
+## role
+Provides static public assets for the frontend web application, including brand identity graphics and reusable UI icons.
+## files
+- favicon.svg | Defines a browser favicon as an SVG graphic featuring a stylized lightning bolt shape with purple and blue gradient glow effects.
+- icons.svg | Defines a collection of reusable SVG icon symbols (Bluesky, Discord, documentation, GitHub, social, X) for use in web applications via `<use>` references.
+## arch
+Flat static asset directory following standard web application conventions, serving files directly at the root URL path without build processing.
+## tags
+favicon, defines, svg, icons, browser, graphic, featuring, stylized
+## symbols
+-
+## workflows
+-
+## dirty
+-