docs: update checkpoints for core policy implementation

docs/checkpoints.md

@@ -50,13 +50,12 @@ Delivered:
 - identifiers module (`packages/core/src/identifiers.js`)
 - targets module (`packages/core/src/targets.js`)
 - authority module (`packages/core/src/authority.js`)
+- policy module (`packages/core/src/policy.js`)
 - target creation, validation, and hierarchy utilities
 - role and capability management
+- policy definitions, decision making, and effect composition
 - comprehensive test suites for all modules
 
-In progress:
-- policy engine
-
 Gate: Complete core implementation before moving to Nostr codecs.
 
 ## Next checkpoint