Add named project snapshots

docs/spec/07-implementation-phases-todo.md

@@ -366,7 +366,9 @@ Tasks:
   update command types
 - [x] expose a cursor-paginated, read-only revision metadata timeline without
   command payloads
-- add named and periodic logical project snapshots
+- [x] add explicitly named logical project snapshots with schema-versioned
+  payloads and integrity checksums
+- add periodic logical project snapshots
 - restore a historical snapshot as a new revision
 - keep database backups separate from logical history
 
@@ -391,6 +393,9 @@ Implemented foundation:
   change-set ids
 - a separate read-only timeline endpoint exposes immutable revision metadata
   in descending, cursor-paginated pages without forward/inverse payloads
+- named snapshot Create/List endpoints persist complete project-scoped runtime
+  state with the source revision and SHA-256 without changing revision or
+  undo/redo stacks
 - a central application dispatcher reconstructs persisted commands and exposes
   optimistic command, undo and redo endpoints for Circuit and CircuitDeviceRow
   field updates