Phase 11.8/12: MIR Core-13 roadmap, Nyash ABI design, async/await enhancements with TaskGroupBox foundation

Major additions:
- Phase 11.8 MIR cleanup specification (Core-15→14→13 roadmap)
- Nyash ABI unified design document (3×u64 structure)
- TaskGroupBox foundation with cancelAll/joinAll methods
- Enhanced async/await with checkpoint auto-insertion
- Structured concurrency preparation (parent-child task relationships)

Documentation:
- docs/development/roadmap/phases/phase-11.8_mir_cleanup/: Complete Core-13 path
- docs/development/roadmap/phases/phase-12/NYASH-ABI-DESIGN.md: Unified ABI spec
- Updated Phase 12 README with AOT/JIT explanation for script performance
- Added async_task_system/ design docs

Implementation progress:
- FutureBox spawn tracking with weak/strong reference management
- VM checkpoint integration before/after await
- LLVM backend async support preparation
- Verifier rules for await-checkpoint enforcement
- Result<T,E> normalization for timeout/cancellation

Technical insights:
- MIR as 'atomic instructions', Box as 'molecules' philosophy
- 'Everything is Box' enables full-stack with minimal instructions
- Unified BoxCall for array/plugin/async operations future consolidation

Next steps:
- Complete TaskGroupBox implementation
- Migrate from global to scoped task management
- Implement LIFO cleanup on scope exit
- Continue Core-13 instruction consolidation

🚀 'From 15 atoms to infinite programs: The Nyash Box Theory'

src/backend/vm_instructions.rs

@@ -589,10 +589,11 @@ impl VM {
         let future_val = self.get_value(future)?;
         
         if let VMValue::Future(ref future_box) = future_val {
-            // This blocks until the future is ready
+            // This blocks until the future is ready (Condvar-based)
             let result = future_box.get();
-            // Convert NyashBox back to VMValue
-            let vm_value = VMValue::from_nyash_box(result);
+            // Wrap into Result.Ok for unified semantics
+            let ok = crate::boxes::result::NyashResultBox::new_ok(result);
+            let vm_value = VMValue::from_nyash_box(Box::new(ok));
             self.set_value(dst, vm_value);
             Ok(ControlFlow::Continue)
         } else {