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.

openspec/changes/archive/unify-tasks-on-services/.pi-map.index.md

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+# openspec/changes/archive/unify-tasks-on-services (index)
+dir: openspec/changes/archive/unify-tasks-on-services
+
+## role
+Archived OpenSpec change proposal that documented the migration of saved task execution from machine-based to SSH service-based references.
+## parent
+index: openspec/changes/archive/.pi-map.index.md
+map: openspec/changes/archive/.pi-map.md
+## children
+-
+## files
+- design.md
+- proposal.md
+- tasks.md
+## links
+index: openspec/changes/archive/unify-tasks-on-services/.pi-map.index.md
+map: openspec/changes/archive/unify-tasks-on-services/.pi-map.md
+## workflows
+-
+## dirty
+-

openspec/changes/archive/unify-tasks-on-services/.pi-map.md

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+# openspec/changes/archive/unify-tasks-on-services
+dir: openspec/changes/archive/unify-tasks-on-services
+
+index: openspec/changes/archive/unify-tasks-on-services/.pi-map.index.md
+
+## role
+Archived OpenSpec change proposal that documented the migration of saved task execution from machine-based to SSH service-based references.
+## files
+- design.md | Design document for unifying saved task execution on SSH services by replacing machine-based references with service-based ones, consolidating history into a single table, and creating a shared backend helper. | dep: ssh_tasks service, service_task_runs table, SettingsStore, ServiceRecord, _build_ssh_client, routers/tasks.py, widgets/sources.py, SshTaskWidgetSource, SQLite 3.25+
+- proposal.md | Proposes migrating the Actions page's saved task execution from machine-based to SSH service-based to unify execution paths with the existing SSH task widget. | dep: ssh_tasks service, service registry, service_task_runs, saved_task_runs, _build_ssh_client, _client_for_machine
+- tasks.md | A completed task plan for refactoring saved tasks to run on SSH services instead of machines, unifying backend and frontend code around a shared runner and service-based execution model. | dep: backend, frontend, SSH services, settings_store, task_runner, routers, widgets, pytest, npm, ruff
+## arch
+Specification-driven change management pattern using three documents (proposal, design, tasks) to capture rationale, technical architecture, and implementation tracking for a completed refactoring effort.
+## tags
+task, execution, ssh, tasks, design, saved, service, backend
+## symbols
+-
+## workflows
+-
+## dirty
+-