Add automatic project snapshots

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

@@ -368,7 +368,7 @@ Tasks:
   command payloads
 - [x] add explicitly named logical project snapshots with schema-versioned
   payloads and integrity checksums
-- add periodic logical project snapshots
+- [x] add periodic logical project snapshots with a bounded retention policy
 - [x] restore a historical snapshot as a new auditable revision with
   persistent undo/redo
 - [x] expose named snapshots, confirmed restore and the paginated revision
@@ -401,6 +401,9 @@ Implemented foundation:
 - 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
+- the central revision boundary captures an `automatic` snapshot after every
+  25 new revisions and retains the newest 12 automatic snapshots per project
+  without deleting named snapshots or immutable revisions
 - the project page lists, creates and explicitly restores named snapshots and
   displays paginated revision metadata without exposing command payloads
 - the version-card header reads persisted undo/redo eligibility and executes