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/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: backend/src
 
 ## role
-Root source directory serving as the main entry point and organizational container for the backend application.
+Core backend application source directory containing server-side business logic, API routes, models, and configuration.
 ## parent
 index: backend/.pi-map.index.md
 map: backend/.pi-map.md