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.

backend/src/media_library_viewer_api/integrations/.pi-map.index.md

@@ -0,0 +1,29 @@
+# backend/src/media_library_viewer_api/integrations (index)
+dir: backend/src/media_library_viewer_api/integrations
+
+## role
+Defines and registers third-party service integrations (e.g., Alertmanager, Grafana, Jellyfin, Prometheus) with typed configs, secrets, and widget definitions for the media library viewer API.
+## parent
+index: backend/src/media_library_viewer_api/.pi-map.index.md
+map: backend/src/media_library_viewer_api/.pi-map.md
+## children
+-
+## files
+- __init__.py
+- alertmanager.py
+- base.py
+- grafana.py
+- jellyfin.py
+- jellyseerr.py
+- nextcloud.py
+- prometheus.py
+- registry.py
+- ssh_tasks.py
+## links
+index: backend/src/media_library_viewer_api/integrations/.pi-map.index.md
+map: backend/src/media_library_viewer_api/integrations/.pi-map.md
+## workflows
+- change integrations behavior
+  read: __init__.py, alertmanager.py, base.py
+## dirty
+-

backend/src/media_library_viewer_api/integrations/.pi-map.md

@@ -0,0 +1,36 @@
+# backend/src/media_library_viewer_api/integrations
+dir: backend/src/media_library_viewer_api/integrations
+
+index: backend/src/media_library_viewer_api/integrations/.pi-map.index.md
+
+## role
+Defines and registers third-party service integrations (e.g., Alertmanager, Grafana, Jellyfin, Prometheus) with typed configs, secrets, and widget definitions for the media library viewer API.
+## files
+- __init__.py | Defines a closed registry module for service integrations.
+- alertmanager.py | Defines the Alertmanager service integration, including connection config, widget definitions, and alert summarization logic. | exp: class:AlertmanagerConfig, class:AlertmanagerAlertsWidgetConfig, func:summarize_alerts(alerts: list[dict[str, Any]], severity_filter) → dict[str, Any], call:alert.get, call:labels.get, call:by_severity.get, call:open_alerts.append, call:annotations.get, call:open_alerts.sort, call:len | dep: typing, media_library_viewer_api.integrations.base
+- base.py | Defines base classes and utilities for creating compile-time service integration definitions with Pydantic-based config schemas, secret fields, and widget kinds. | exp: class:ServiceConfigBase, class:WidgetConfigBase, class:SecretField, class:WidgetKind, class:ServiceDefinition, method:widget_kind(self, kind: str) → WidgetKind | None, func:widget_kind(kind: str, name: str, description: str, model_cls: type[WidgetConfigBase], default_config, refresh_interval_ms) → WidgetKind, call:model_cls.model_json_schema, call:schema.pop, call:WidgetKind, call:dict, func:validate_config(model_cls: type[BaseModel], config: dict[str, Any] | None) → dict[str, Any], call:model_cls.model_validate, call:instance.model_dump | dep: dataclasses, typing, pydantic
+- grafana.py | Defines the Grafana service configuration, secret fields, and widget types for integration with the media library viewer API. | exp: class:GrafanaConfig, class:GrafanaLinkWidgetConfig | dep: media_library_viewer_api.integrations.base
+- jellyfin.py | Defines the Jellyfin media server service configuration and activity widget definition for a media library viewer API. | exp: class:JellyfinConfig, class:JellyfinActivityWidgetConfig | dep: media_library_viewer_api.integrations.base
+- jellyseerr.py | Defines a service configuration and metadata for Jellyseerr, a request management companion to Jellyfin. | exp: class:JellyseerrConfig | dep: media_library_viewer_api.integrations.base
+- nextcloud.py | Defines the Nextcloud service configuration model and service definition for integration into the media library viewer API. | exp: class:NextcloudConfig | dep: media_library_viewer_api.integrations.base
+- prometheus.py | Defines the service configuration, widget types, and service definition for integrating Prometheus as a metrics data source. | exp: class:PrometheusConfig, class:PrometheusMetricWidgetConfig | dep: media_library_viewer_api.integrations.base
+- registry.py | Provides a closed registry of service definitions with lookup and enumeration functions. | exp: func:list_service_types() → list[str], call:sorted, func:get_service_definition(service_type: str) → ServiceDefinition | None, call:SERVICE_DEFINITIONS.get, func:get_widget_kind(service_type: str, widget_kind: str) → WidgetKind | None, call:get_service_definition, call:definition.widget_kind, func:require_service_definition(service_type: str) → ServiceDefinition, call:get_service_definition, raise:ValueError | dep: media_library_viewer_api.integrations.alertmanager, media_library_viewer_api.integrations.base, media_library_viewer_api.integrations.grafana, media_library_viewer_api.integrations.jellyfin, media_library_viewer_api.integrations.jellyseerr, media_library_viewer_api.integrations.nextcloud, media_library_viewer_api.integrations.prometheus, media_library_viewer_api.integrations.ssh_tasks
+- ssh_tasks.py | Defines a service configuration for an SSH task runner that executes reusable saved tasks over SSH and records run history. | exp: class:SshTasksConfig, class:SshTaskOutputWidgetConfig | dep: media_library_viewer_api.integrations.base
+## arch
+Plugin/registry pattern using Pydantic-based config schemas with a closed registry for compile-time service definition lookups, base class extension for per-service widgets and secrets, and a modular file-per-integration structure.
+## tags
+config, service, widget, integrations, media_library_viewer_api, base, definition, kind
+## symbols
+- AlertmanagerConfig
+- AlertmanagerAlertsWidgetConfig
+- ServiceConfigBase
+- WidgetConfigBase
+- SecretField
+- WidgetKind
+- ServiceDefinition
+- GrafanaConfig
+## workflows
+- change integrations behavior
+  read: __init__.py, alertmanager.py, base.py
+## dirty
+-