Expose project version history

docs/project-history-and-external-model-architecture.md

@@ -97,6 +97,9 @@ Implemented named-snapshot foundation:
   separately and are never imported into the logical snapshot payload
 - arbitrary restore payloads are rejected by the generic user-command
   endpoint; only server-stored snapshots can initiate a forward restore
+- the project page provides an initially collapsed snapshot/timeline panel,
+  explicit inline restore confirmation and cursor-based loading of older
+  revisions; a successful restore reloads all project read models
 
 ## Revit / CSV / IFCGUID Round-Trip Direction
 
@@ -252,7 +255,7 @@ Completed foundation:
 
 Remaining constraints before completing project version history:
 
-- add a browsable timeline/snapshot UI and periodic snapshot policy
+- define and implement a periodic snapshot and retention policy
 - extend project-scoped commands only when further project mutations are
   deliberately added to history; the generic versioned envelope is complete
 - do not model IFCGUID as an overloaded circuit equipment identifier