add JSON and crypto APIs with sandbox protection (milestone 6 complete)

SANDBOX_MILESTONES.md

@@ -202,8 +202,9 @@ TEST(SafeRequire, CachesModules);
 
 ---
 
-## Milestone 5: Timer & Callback System
+## Milestone 5: Timer & Callback System ✅
 
+**Status**: Complete
 **Goal**: Safe timer APIs managed by kernel.
 **Estimated Files**: 1 new file
 
@@ -251,8 +252,9 @@ TEST(TimerManager, CleansUpOnStop);
 
 ---
 
-## Milestone 6: JSON & Crypto APIs
+## Milestone 6: JSON & Crypto APIs ✅
 
+**Status**: Complete
 **Goal**: Safe data parsing and cryptographic primitives.
 **Estimated Files**: 2 new files