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/prometheus/.pi-map.index.md

@@ -0,0 +1,24 @@
+# monitoring/prometheus (index)
+dir: monitoring/prometheus
+
+## role
+Provides configuration for standalone Prometheus deployments to scrape and collect metrics from local infrastructure services and remote nodes.
+## parent
+index: monitoring/.pi-map.index.md
+map: monitoring/.pi-map.md
+## children
+- monitoring/prometheus/file-sd
+  index: monitoring/prometheus/file-sd/.pi-map.index.md
+  map: monitoring/prometheus/file-sd/.pi-map.md
+- monitoring/prometheus/rules
+  index: monitoring/prometheus/rules/.pi-map.index.md
+  map: monitoring/prometheus/rules/.pi-map.md
+## files
+- prometheus.standalone.yml
+## links
+index: monitoring/prometheus/.pi-map.index.md
+map: monitoring/prometheus/.pi-map.md
+## workflows
+-
+## dirty
+-

monitoring/prometheus/.pi-map.md

@@ -0,0 +1,19 @@
+# monitoring/prometheus
+dir: monitoring/prometheus
+
+index: monitoring/prometheus/.pi-map.index.md
+
+## role
+Provides configuration for standalone Prometheus deployments to scrape and collect metrics from local infrastructure services and remote nodes.
+## files
+- prometheus.standalone.yml | Configures Prometheus monitoring server to scrape metrics from itself, node exporters, Loki, Alertmanager, Grafana, and remote nodes via file-based service discovery | dep: alertmanager, node-exporter, loki, grafana, file-sd
+## arch
+Uses a declarative static YAML configuration pattern leveraging file-based service discovery for dynamic remote target management.
+## tags
+node, loki, alertmanager, grafana, prometheus.standalone, configures, prometheus, monitoring
+## symbols
+-
+## workflows
+-
+## dirty
+-

monitoring/prometheus/file-sd/.pi-map.index.md

@@ -0,0 +1,19 @@
+# monitoring/prometheus/file-sd (index)
+dir: monitoring/prometheus/file-sd
+
+## role
+Provides static target configuration for Prometheus to discover and scrape node_exporter metrics endpoints.
+## parent
+index: monitoring/prometheus/.pi-map.index.md
+map: monitoring/prometheus/.pi-map.md
+## children
+-
+## files
+- node_exporter_targets.json
+## links
+index: monitoring/prometheus/file-sd/.pi-map.index.md
+map: monitoring/prometheus/file-sd/.pi-map.md
+## workflows
+-
+## dirty
+-

monitoring/prometheus/file-sd/.pi-map.md

@@ -0,0 +1,19 @@
+# monitoring/prometheus/file-sd
+dir: monitoring/prometheus/file-sd
+
+index: monitoring/prometheus/file-sd/.pi-map.index.md
+
+## role
+Provides static target configuration for Prometheus to discover and scrape node_exporter metrics endpoints.
+## files
+- node_exporter_targets.json | Empty JSON file intended to define scrape targets for Prometheus node_exporter | dep: Prometheus, node_exporter
+## arch
+Uses the Prometheus file-based service discovery (file_sd) pattern with JSON-formatted target definitions.
+## tags
+targets, node, exporter, prometheus, empty, json, intended, define
+## symbols
+-
+## workflows
+-
+## dirty
+-

monitoring/prometheus/rules/.pi-map.index.md

@@ -0,0 +1,19 @@
+# monitoring/prometheus/rules (index)
+dir: monitoring/prometheus/rules
+
+## role
+Defines Prometheus alerting rules for monitoring backup job failures and observability stack health.
+## parent
+index: monitoring/prometheus/.pi-map.index.md
+map: monitoring/prometheus/.pi-map.md
+## children
+-
+## files
+- backup_alerts.yml
+## links
+index: monitoring/prometheus/rules/.pi-map.index.md
+map: monitoring/prometheus/rules/.pi-map.md
+## workflows
+-
+## dirty
+-

monitoring/prometheus/rules/.pi-map.md

@@ -0,0 +1,19 @@
+# monitoring/prometheus/rules
+dir: monitoring/prometheus/rules
+
+index: monitoring/prometheus/rules/.pi-map.index.md
+
+## role
+Defines Prometheus alerting rules for monitoring backup job failures and observability stack health.
+## files
+- backup_alerts.yml | Defines Prometheus alerting rules for backup job failures and observability stack health monitoring. | dep: Prometheus, Alertmanager, Grafana, manage_backup_runs_total metric, manage_backup_runs_last_success_timestamp metric, up metric
+## arch
+Configuration-as-code pattern using declarative YAML rule files consumed directly by the Prometheus alerting engine.
+## tags
+backup, prometheus, alerts, defines, alerting, rules, job, failures
+## symbols
+-
+## workflows
+-
+## dirty
+-