chore: regenerate stale .pi-map.md / .pi-map.index.md project maps

Project map had drifted: claimed recharts unused (was used), ObservabilityPage.tsx
exists (refactored to service-tabs/), missed JellyfinNowPlayingWidget +
authentik/backups service types. Regenerate to reflect post-change reality:
new Qbittorrent/LineSeriesChart/Prometheus{Gauge,Mean}Widget files,
service_data.py/qbittorrent_store.py, canonical prometheus-charting +
service-storage specs, archived changes.

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

@@ -2,7 +2,7 @@
 dir: backend/src/media_library_viewer_api/widgets
 
 ## role
-Provides widget definitions, schemas, and data source adapters for rendering configurable dashboard widgets from both built-in and external service data.
+Widget subsystem providing configurable dashboard widget definitions, source adapters, and data transformation helpers 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
@@ -11,12 +11,13 @@ map: backend/src/media_library_viewer_api/.pi-map.md
 ## files
 - __init__.py
 - builtin.py
+- prometheus_range.py
 - sources.py
 ## links
 index: backend/src/media_library_viewer_api/widgets/.pi-map.index.md
 map: backend/src/media_library_viewer_api/widgets/.pi-map.md
 ## workflows
 - change widgets behavior
-  read: __init__.py, builtin.py, sources.py
+  read: __init__.py, builtin.py, prometheus_range.py
 ## dirty
 -