docs: update Phase 7 planning and add correct Nyash philosophy test files

- Update CLAUDE.md with 32-thread build option
- Enhance phase7_async_mir.md with detailed implementation plan
- Add Obj class definition to phase6_ref_set_get.nyash
- Create phase6_ref_set_get_correct.nyash following Everything is Box philosophy

local_tests/phase6_ref_set_get.nyash

@@ -1,3 +1,8 @@
+// Phase 6.1 test: Object creation and field access
+box Obj {
+  init { x }
+}
+
 static box Main {
   main() {
     local o

local_tests/phase6_ref_set_get_correct.nyash

@@ -0,0 +1,14 @@
+// Phase 6.1 test: Object creation and field access (Nyash哲学準拠版)
+box DataBox {
+  init { value }
+}
+
+static box Main {
+  main() {
+    local data
+    data = new DataBox()
+    data.value = 1
+    print(data.value)
+    return data.value
+  }
+}