Bring documentation in line with integrated features

List the building structure, room areas, rough power balance and cable
sizing in the README and documentation map, add an architecture section
for the rough power balance, correct stale snapshot schema references and
record the integrated contributor features in the backlog.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/spec/08-current-product-backlog.md

@@ -135,6 +135,25 @@ The pre-release cleanup established the following compatibility boundary:
 - [x] Keep column visibility and order as a project-specific UI preference so
   all distribution boards in the same project open with the same columns.
 
+## Integrated Contributor Features (September 2026)
+
+- [x] Client ids without secure-context browser APIs (`createClientId`).
+- [x] Icon actions, compact column headers and the AMEV picker in the circuit
+  list; icon actions and collapsible filters on the project overview.
+- [x] Print view with cover, board overview, board plans, board info card and
+  office branding.
+- [x] Buildings above floors and a dedicated building structure page.
+- [x] Optional net room area with sums per floor and building.
+- [x] Optional cable-sizing module for one circuit on demand
+  (DIN VDE 0298-4:2023-06 with Berichtigung 1).
+- [x] Rough power balance for LPH 2/3 by cost group, including the comparison
+  with the detailed balance and the explicit copy of one row as a
+  ProjectDevice.
+
+Open follow-ups (Gitea issues): logical feed link between distribution boards
+(#3), bill of quantities export (#5), area-based loads in W/m² for
+ProjectDevices and device rows (#20).
+
 ## Recommended Sequence
 
 1. [x] Distribution-board floor and supply fields.