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.md

@@ -4,10 +4,10 @@ dir: backend/src
 index: backend/src/.pi-map.index.md
 
 ## 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.
 ## files
 ## arch
-Standard layered architecture entry point, typically initializing the application, wiring up configurations, modules, routes, and services (e.g., MVC, modular monolith, or Clean Architecture).
+Cannot be fully determined as no files are listed in the directory; likely follows standard Node.js/Python backend patterns (e.g., MVC, layered architecture) depending on framework used.
 ## tags
 -
 ## symbols