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/domain/.pi-map.index.md

@@ -0,0 +1,22 @@
+# backend/src/media_library_viewer_api/domain (index)
+dir: backend/src/media_library_viewer_api/domain
+
+## role
+Domain layer providing data normalization and transformation helpers for Jellyfin media data and dashboard summaries.
+## 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
+- dashboard.py
+- media.py
+## links
+index: backend/src/media_library_viewer_api/domain/.pi-map.index.md
+map: backend/src/media_library_viewer_api/domain/.pi-map.md
+## workflows
+- change domain behavior
+  read: __init__.py, dashboard.py, media.py
+## dirty
+-

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

@@ -0,0 +1,29 @@
+# backend/src/media_library_viewer_api/domain
+dir: backend/src/media_library_viewer_api/domain
+
+index: backend/src/media_library_viewer_api/domain/.pi-map.index.md
+
+## role
+Domain layer providing data normalization and transformation helpers for Jellyfin media data and dashboard summaries.
+## files
+- __init__.py | Swaps the position of two tmux panes within a window or between windows | dep: tmux, sh
+- dashboard.py | Provides domain helper functions for building dashboard data, specifically normalizing Jellyfin session activity rows and computing backup job summaries. | exp: func:_map_sessions_to_activity_rows(sessions: list[dict[str, Any]]) → list[dict[str, Any]], call:session.get, call:bool, call:item.get, call:play_state.get, call:transcoding.get, call:transcode_type.append, call:results.append, call:", ".join, func:build_backup_dashboard_summary(store: SettingsStore) → BackupDashboardSummary, call:store.list_backup_jobs, call:len, call:int, call:time.time, call:store.list_backup_runs, call:recent_runs.append, call:sum, call:store.list_backup_alerts, call:failed_runs.append, call:max, call:BackupDashboardSummary, call:round | dep: time, typing, media_library_viewer_api.models.backups, media_library_viewer_api.services.settings_store
+- media.py | Flattens inconsistent Jellyfin API JSON into normalized dictionaries for SQLite indexing and frontend display. | exp: func:first_media_source(item: dict[str, Any]) → dict[str, Any], call:item.get, func:media_streams(item: dict[str, Any], stream_type) → list[dict[str, Any]], call:item.get, call:streams.extend, call:source.get, call:str(stream.get("Type") or stream.get("codec_type") or "").lower, call:stream.get, call:stream_type.lower, func:stream_value(stream: dict[str, Any], *keys: str) → Any, func:is_hdr_item(item: dict[str, Any]) → bool, call:media_streams, call:stream_value, call:" ".join, call:str(value).lower, call:any, func:format_date_added(value: str | None) → str, call:pd.to_datetime(value).strftime, call:str, func:timestamp_date_added(value: str | None) → int | None, call:int, call:pd.to_datetime(value).timestamp, func:format_rate_bits_decimal(bits_per_second: float | int | str | None) → str, call:float, call:str, func:normalize_media_item(item: dict[str, Any], library_id, library_name) → dict[str, Any], call:first_media_source, call:media_streams, call:source.get, call:item.get, call:stream_value, call:is_hdr_item, call:int, call:ticks_to_minutes, call:human_size, call:format_rate_bits_decimal, call:video.get, call:format_date_added, call:timestamp_date_added, func:display_media_row(row: dict[str, Any]) → dict[str, Any], call:row.get, call:human_size, call:format_rate_bits_decimal | dep: typing, media_library_viewer_api.utils, pandas
+## arch
+Stateless functional modules that transform inconsistent upstream API JSON into normalized dictionaries for persistence and display.
+## tags
+media, backup, call:item.get, call:str, date, added, dashboard, call:store.list
+## symbols
+- _map_sessions_to_activity_rows
+- build_backup_dashboard_summary
+- first_media_source
+- media_streams
+- stream_value
+- is_hdr_item
+- format_date_added
+- timestamp_date_added
+## workflows
+- change domain behavior
+  read: __init__.py, dashboard.py, media.py
+## dirty
+-