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/skills/openspec-propose/.pi-map.index.md

@@ -0,0 +1,19 @@
+# .opencode/skills/openspec-propose (index)
+dir: .opencode/skills/openspec-propose
+
+## role
+Provides an AI assistant skill that automates the openspec proposal workflow by scaffolding directories and generating structured artifacts (proposals, designs, tasks).
+## parent
+index: .opencode/skills/.pi-map.index.md
+map: .opencode/skills/.pi-map.md
+## children
+-
+## files
+- SKILL.md
+## links
+index: .opencode/skills/openspec-propose/.pi-map.index.md
+map: .opencode/skills/openspec-propose/.pi-map.md
+## workflows
+-
+## dirty
+-