Add automatic project snapshots

docs/circuit-list-editor-api.md

@@ -33,7 +33,8 @@ this value for optimistic concurrency checks.
   - executes the eligible inverse or forward command as a new auditable
     revision
 - `GET /projects/:projectId/snapshots`
-  - lists named logical snapshot metadata without returning payload JSON
+  - lists named and automatic logical snapshot metadata, including `kind`,
+    without returning payload JSON
 - `POST /projects/:projectId/snapshots`
   - body:
     `{ "expectedRevision": 12, "name": "Vor Ausschreibung", "description": "Optional" }`
@@ -44,6 +45,9 @@ this value for optimistic concurrency checks.
   - snapshot creation does not increment the project revision or alter
     undo/redo stacks
   - duplicate names and stale revisions return `409`
+  - the central revision boundary additionally creates `automatic` snapshots
+    after 25 further revisions and retains the newest 12 per project; named
+    snapshots are never removed by this policy
 - `POST /projects/:projectId/snapshots/:snapshotId/restore`
   - body: `{ "expectedRevision": 13 }`
   - verifies the stored payload checksum and atomically restores the complete