v0.7.2: undo/redo — TDD

Operation-level memory undo/redo built on existing Merkle snapshot
infrastructure. undo-snapshot captures state before destructive tool
execution. /undo and /redo TUI commands send structured events.

- core-memory: undo-snapshot, undo, redo functions + 3 tests
- core-perceive: :undo/:redo sensor handlers
- core-act: auto-snapshot before non-read-only tools
- core-package: undo/redo symbol exports
- channel-tui-main: /undo, /redo commands + 2 tests
- Core: 73/73  TUI Main: 74/74

org/core-package.org

@@ -62,6 +62,11 @@ The package definition. All public symbols are exported here.
    #:memory-object-scope
    #:snapshot-memory
    #:rollback-memory
+   #:undo-snapshot
+   #:undo
+   #:redo
+   #:*undo-stack*
+   #:*redo-stack*
     #:context-get-system-logs
     #:context-assemble-global-awareness
     #:context-awareness-assemble