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_node.py

@@ -0,0 +1,93 @@
+"""
+tests/test_node.py
+CTNode 단위 테스트
+"""
+
+import pytest
+from ctstruct import CTNode, NodeType
+
+
+class TestCTNodeBasic:
+    def test_create_node(self):
+        n = CTNode(NodeType.PARAGRAPH, "hello")
+        assert n.node_type == NodeType.PARAGRAPH
+        assert n.content == "hello"
+        assert n.is_leaf
+        assert n.is_root
+
+    def test_append_child(self):
+        parent = CTNode(NodeType.SECTION)
+        child = CTNode(NodeType.PARAGRAPH, "child")
+        parent.append(child)
+        assert len(parent) == 1
+        assert child.parent is parent
+        assert not parent.is_leaf
+
+    def test_depth(self):
+        root = CTNode(NodeType.ROOT)
+        sec = CTNode(NodeType.SECTION)
+        para = CTNode(NodeType.PARAGRAPH, "text")
+        root.append(sec)
+        sec.append(para)
+        assert root.depth == 0
+        assert sec.depth == 1
+        assert para.depth == 2
+
+    def test_detach(self):
+        parent = CTNode(NodeType.SECTION)
+        child = CTNode(NodeType.PARAGRAPH, "bye")
+        parent.append(child)
+        child.detach()
+        assert len(parent) == 0
+        assert child.parent is None
+
+    def test_walk_pre(self):
+        root = CTNode(NodeType.ROOT)
+        a = CTNode(NodeType.SECTION)
+        b = CTNode(NodeType.PARAGRAPH, "b")
+        root.append(a)
+        a.append(b)
+        nodes = list(root.walk("pre"))
+        assert nodes[0] is root
+        assert nodes[1] is a
+        assert nodes[2] is b
+
+    def test_walk_bfs(self):
+        root = CTNode(NodeType.ROOT)
+        a = CTNode(NodeType.SECTION)
+        b = CTNode(NodeType.PARAGRAPH, "b")
+        c = CTNode(NodeType.PARAGRAPH, "c")
+        root.append(a)
+        root.append(c)
+        a.append(b)
+        bfs = list(root.walk("bfs"))
+        assert bfs[0] is root
+        # level 1: a, c
+        assert bfs[1] is a
+        assert bfs[2] is c
+        # level 2: b
+        assert bfs[3] is b
+
+    def test_find(self):
+        root = CTNode(NodeType.ROOT)
+        root.append(CTNode(NodeType.HEADING, "h1", {"level": 1}))
+        root.append(CTNode(NodeType.PARAGRAPH, "para"))
+        root.append(CTNode(NodeType.HEADING, "h2", {"level": 2}))
+        headings = root.find(NodeType.HEADING)
+        assert len(headings) == 2
+
+    def test_text_content(self):
+        root = CTNode(NodeType.ROOT)
+        root.append(CTNode(NodeType.PARAGRAPH, "hello "))
+        root.append(CTNode(NodeType.PARAGRAPH, "world"))
+        assert root.text_content() == "hello world"
+
+    def test_siblings(self):
+        parent = CTNode(NodeType.SECTION)
+        a = CTNode(NodeType.PARAGRAPH, "a")
+        b = CTNode(NodeType.PARAGRAPH, "b")
+        c = CTNode(NodeType.PARAGRAPH, "c")
+        parent.append(a)
+        parent.append(b)
+        parent.append(c)
+        assert b.siblings == [a, c]