Document protected circuit groups

docs/circuit-list-editor-architecture.md

@@ -17,13 +17,15 @@ The pure grid modules have no React state and are covered by focused unit tests.
 ## Domain Model Overview
 
 - `CircuitSection`
-  - Groups circuits by planning section (for example lighting, single-phase, three-phase).
-  - Owns section metadata (`key`, `displayName`, `prefix`, ordering).
+  - Represents a protected circuit group in one of the categories lighting,
+    single-phase or three-phase.
+  - Owns category, positive group number, generated prefix, display name and
+    ordering.
 - `Circuit`
   - Core electrical unit in the list.
   - Owns circuit-level identifiers and technical data:
     - `equipmentIdentifier` (BMK)
-    - protection data
+    - one explicit one-to-one protection device
     - cable data
     - reserve state
     - voltage and optional control requirement for future sizing
@@ -43,6 +45,10 @@ The pure grid modules have no React state and are covered by focused unit tests.
 - `ProjectDevice`
   - Reusable device template entity at project level.
   - Can be linked to `CircuitDeviceRow` entries, with copied display values on insert.
+- `DistributionBoardComponent`
+  - Represents fixed header components, optional group protection and manually
+    named auxiliary footer devices with their own unique BMK.
+  - Group protection may own a separate one-to-one protection configuration.
 - Retained legacy migration source
   - Old `consumers` rows, mappings and reports are available only to explicit
     database upgrade tooling.
@@ -77,7 +83,9 @@ Section-level `-frei-` placeholder rows represent insertion targets for creating
 `equipmentIdentifier` / BMK is circuit-owned (`Circuit.equipmentIdentifier`).
 
 - Device rows do not have their own BMK.
-- Existing identifiers must stay stable unless explicitly changed by user action.
+- Existing identifiers stay stable on sort, insert and delete. Explicit
+  renumbering may change them, and a user-initiated complete-circuit move to
+  another same-category group assigns the next target-group identifier.
 - Renumbering is explicit, not implicit on move/sort/delete.
 
 ## Data Ownership Split: Circuit vs Device Row
@@ -113,9 +121,9 @@ The sibling `/tree` route is a read-only structure preview. Old
 
 ## Future Persistence Direction
 
-Persistent undo/redo, project revisions, logical snapshots, external-model exchange and PostgreSQL readiness are specified in [Project History and External Model Architecture](./project-history-and-external-model-architecture.md).
-
-Critical multi-write commands already use explicit persistence transaction
-adapters. The next step is to compose these command boundaries into server-side,
-project-scoped revisions and change sets. Database backups remain separate from
-user-visible project snapshots.
+Persistent Undo/Redo, project revisions and logical snapshots are implemented
+through project-scoped commands and the shared transaction boundary. Database
+backups remain separate from user-visible project snapshots. External-model
+exchange and PostgreSQL readiness are specified in
+[Project History and External Model Architecture](./project-history-and-external-model-architecture.md)
+and remain future work.