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.

.opencode/commands/.pi-map.index.md

@@ -0,0 +1,22 @@
+# .opencode/commands (index)
+dir: .opencode/commands
+
+## role
+Defines slash-command workflows and assistant personas for an OpenSpec-based development process (explore, propose, apply, archive).
+## parent
+index: .opencode/.pi-map.index.md
+map: .opencode/.pi-map.md
+## children
+-
+## files
+- opsx-apply.md
+- opsx-archive.md
+- opsx-explore.md
+- opsx-propose.md
+## links
+index: .opencode/commands/.pi-map.index.md
+map: .opencode/commands/.pi-map.md
+## workflows
+-
+## dirty
+-