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.

monitoring/alloy/.pi-map.index.md

@@ -0,0 +1,19 @@
+# monitoring/alloy (index)
+dir: monitoring/alloy
+
+## role
+Centralized log collection configuration that scrapes Docker container logs and forwards them to Loki for storage and querying.
+## parent
+index: monitoring/.pi-map.index.md
+map: monitoring/.pi-map.md
+## children
+-
+## files
+- config.alloy
+## links
+index: monitoring/alloy/.pi-map.index.md
+map: monitoring/alloy/.pi-map.md
+## workflows
+-
+## dirty
+-

monitoring/alloy/.pi-map.md

@@ -0,0 +1,19 @@
+# monitoring/alloy
+dir: monitoring/alloy
+
+index: monitoring/alloy/.pi-map.index.md
+
+## role
+Centralized log collection configuration that scrapes Docker container logs and forwards them to Loki for storage and querying.
+## files
+- config.alloy | Configures Alloy to scrape Docker container logs and forward them to a local Loki instance | dep: docker, loki, discovery.docker, discovery.relabel, loki.source.docker, loki.write
+## arch
+Declarative agent-based collection pattern using Grafana Alloy's discovery and pipeline stages to discover containers, tail their logs, and stream them to a local Loki destination.
+## tags
+docker, loki, discovery, config, configures, alloy, scrape, container
+## symbols
+-
+## workflows
+-
+## dirty
+-