docs: reorganize into 説明書/予定/archive; update docs/README.md and CLAUDE.md; move root .nyash to local_tests; consolidate native-plan notes into README + archive

local_tests/test_array_box_simple.nyash

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+// 🧪 ArrayBoxの簡単なテスト
+
+print("=== ArrayBox Simple Test ===")
+local arr
+arr = new ArrayBox()
+
+// 基本的な操作
+arr.push("Hello")
+arr.push("World")
+print("Length: " + arr.length())
+print("Get 0: " + arr.get(0))
+print("Get 1: " + arr.get(1))
+
+// pop
+local item
+item = arr.pop()
+print("Popped: " + item)
+print("Length after pop: " + arr.length())
+
+print("Test completed!")