feat: initial CTStruct framework

- CTNode: 트리 기본 단위 (전위/후위/BFS 순회, 탐색, 분리)
- CTTree: 트리 컨테이너 (빌더 API, TOC, filter/map/merge)
- NodeType: 구조/블록/인라인/메타 노드 타입 Enum
- MarkdownParser: Markdown → CTTree 파서
- MarkdownRenderer: CTTree → Markdown 렌더러
- JSONRenderer: CTTree → JSON 직렬화
- 27개 단위/통합 테스트 전체 통과

tests/test_tree.py

@@ -0,0 +1,70 @@
+"""
+tests/test_tree.py
+CTTree 단위 테스트
+"""
+
+import json
+import pytest
+from ctstruct import CTTree, CTNode, NodeType
+
+
+class TestCTTree:
+    def test_add_node(self):
+        tree = CTTree("My Doc")
+        tree.add(NodeType.PARAGRAPH, "hello")
+        assert len(tree) == 1
+
+    def test_make_list(self):
+        lst = CTTree.make_list(["A", "B", "C"])
+        assert lst.node_type == NodeType.LIST
+        assert len(lst) == 3
+        assert lst[0].content == "A"
+
+    def test_make_table(self):
+        table = CTTree.make_table(
+            headers=["이름", "나이"],
+            rows=[["Alice", "30"], ["Bob", "25"]],
+        )
+        assert table.node_type == NodeType.TABLE
+        assert len(table) == 3  # 헤더행 + 2행
+
+    def test_toc(self):
+        tree = CTTree()
+        tree.add(NodeType.HEADING, "서론", level=1)
+        tree.add(NodeType.HEADING, "본론", level=2)
+        tree.add(NodeType.HEADING, "결론", level=1)
+        toc = tree.toc()
+        assert len(toc) == 3
+        assert toc[0]["text"] == "서론"
+
+    def test_to_dict_and_back(self):
+        tree = CTTree("Test")
+        tree.add(NodeType.PARAGRAPH, "테스트 문단")
+        d = tree.to_dict()
+        restored = CTTree.from_dict(d)
+        paras = restored.find(NodeType.PARAGRAPH)
+        assert len(paras) == 1
+        assert paras[0].content == "테스트 문단"
+
+    def test_filter(self):
+        tree = CTTree()
+        tree.add(NodeType.HEADING, "H", level=1)
+        tree.add(NodeType.PARAGRAPH, "P")
+        filtered = tree.filter(lambda n: n.node_type != NodeType.PARAGRAPH)
+        assert len(filtered.find(NodeType.PARAGRAPH)) == 0
+        assert len(filtered.find(NodeType.HEADING)) == 1
+
+    def test_merge(self):
+        t1 = CTTree()
+        t1.add(NodeType.PARAGRAPH, "t1")
+        t2 = CTTree()
+        t2.add(NodeType.PARAGRAPH, "t2")
+        t1.merge(t2)
+        assert len(t1.find(NodeType.PARAGRAPH)) == 2
+
+    def test_node_count(self):
+        tree = CTTree()
+        tree.add(NodeType.PARAGRAPH, "a")
+        tree.add(NodeType.PARAGRAPH, "b")
+        # root(1) + 2 paragraphs
+        assert tree.node_count == 3